UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

For the period ended September 30, 2007

OR

For the transition period from         to         

Commission file number 1-8993

WHITE MOUNTAINS INSURANCE GROUP, LTD.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code:  (603) 640-2200

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.

Yes x     No o

Indicate by check mark whether the Registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definition of “accelerated filer and large accelerated filer” in Rule 12b-2 of the Exchange Act.

Large accelerated filer x          Accelerated filer o                                                   Non-accelerated filer o

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).

Yes o     No x

As of November 2, 2007, 10,560,272 common shares with a par value of $1.00 per share were outstanding (which includes 54,000 restricted common shares that were not vested at such date).

WHITE MOUNTAINS INSURANCE GROUP, LTD.

Table of Contents

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PART I. FINANCIAL INFORMATION.

Item 1. Financial Statements

WHITE MOUNTAINS INSURANCE GROUP, LTD.

CONSOLIDATED BALANCE SHEETS

See Notes to Consolidated Financial Statements

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WHITE MOUNTAINS INSURANCE GROUP, LTD.

CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME

Unaudited

See Notes to Consolidated Financial Statements

4

WHITE MOUNTAINS INSURANCE GROUP, LTD.

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS’ EQUITY

Unaudited

See Notes to Consolidated Financial Statements

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WHITE MOUNTAINS INSURANCE GROUP, LTD.

CONSOLIDATED STATEMENTS OF CASH FLOWS

Unaudited

See Notes to Consolidated Financial Statements

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NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (Unaudited)

Note 1. Summary of Significant Accounting Policies

Basis of presentation

These interim consolidated financial statements include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) and its subsidiaries (collectively with the Company, “White Mountains”) and have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its property and casualty insurance and reinsurance subsidiaries and affiliates. The Company’s headquarters are located at Bank of Butterfield Building, 42 Reid Street, Hamilton, Bermuda HM 12, its principal executive office is located at 80 South Main Street, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11.  White Mountains’ reportable segments are OneBeacon, White Mountains Re, Esurance and Other Operations.  Significant transactions among White Mountains’ segments have been eliminated in this report.

The OneBeacon segment consists of OneBeacon Insurance Group, Ltd. (“OneBeacon Ltd.”), an exempted Bermuda limited liability company that owns a family of U.S.-based property and casualty insurance companies (collectively “OneBeacon”), substantially all of which operate in a multi-company pool. OneBeacon offers a wide range of specialty, personal and commercial products and services sold primarily through select independent agents and brokers. OneBeacon was acquired by White Mountains in 2001 (the “OneBeacon Acquisition”).  During the fourth quarter of 2006, White Mountains sold 27.6 million, or 27.6%, of OneBeacon Ltd.’s common shares in an initial public offering (the “OneBeacon Offering”).  In connection with the OneBeacon Offering, White Mountains undertook an internal reorganization (the “Reorganization”) and formed OneBeacon Ltd. for the purpose of holding certain of its property and casualty insurance businesses. As a result of the Reorganization, certain of White Mountains’ businesses that had been historically reported as part of its Other Operations segment are now owned by OneBeacon Ltd., and accordingly have been included in the OneBeacon segment for all periods presented in this report.  In addition, certain other businesses of White Mountains that had been historically reported as part of its OneBeacon segment and which were not held by OneBeacon Ltd. following the OneBeacon Offering are included in the Other Operations segment for all periods presented in this report.

The White Mountains Re segment consists of White Mountains Re Ltd., an exempted Bermuda limited liability company, and its subsidiaries (collectively, “White Mountains Re”).  White Mountains Re offers reinsurance capacity for property, liability, accident & health, aviation and certain other exposures on a worldwide basis through its subsidiaries, Folksamerica Reinsurance Company (“Folksamerica Re”, together with its immediate parent, Folksamerica Holding Company (“Folksamerica Holdings”), “Folksamerica”), Sirius International Insurance Corporation (“Sirius International”) and Fund American Reinsurance Company, Ltd. (“FARe”).  White Mountains Re also provides reinsurance advisory services, specializing primarily in property and other short-tailed lines of reinsurance, through White Mountains Re Underwriting Services Ltd. (“WMRUS”).  On August 3, 2006, White Mountains Re sold one of its subsidiaries, Sirius America Insurance Company (“Sirius America”), to an investor group.  As part of the transaction, White Mountains acquired an equity interest of approximately 18% in the acquiring entity, Lightyear Delos Acquisition Corp. (“Delos”), and accounts for Delos on the equity method within its Other Operations segment.

The Esurance segment consists of Esurance Holdings, Inc., and its subsidiaries (collectively, “Esurance”). Esurance sells personal auto insurance directly to customers online and through select online agents.

White Mountains’ Other Operations segment consists of the Company and its intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), its weather risk management business (“Galileo”), its variable annuity reinsurance business, White Mountains Life Reinsurance (Bermuda) Ltd. (“WM Life Re”), as well as the International American Group, Inc. (the “International American Group”) and various other entities not included in other segments. The International American Group, which was acquired by White Mountains in 1999, includes American Centennial Insurance Company (“American Centennial”) and British Insurance Company of Cayman (“British Insurance Company”), both of which are in run-off.  The Other Operations segment also includes White Mountains’ investments in common shares and warrants to purchase common shares of Symetra Financial Corporation (“Symetra”), the consolidated results of the Tuckerman Capital, LP and Tuckerman Capital II, LP funds (“Tuckerman Funds”), common and preferred shares of Delos and warrants to purchase common shares of Montpelier Re Holdings, Ltd. (“Montpelier Re”), which White Mountains sold back to Montpelier Re on May 1, 2007.

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All significant intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly present the financial position, results of operations and cash flows of White Mountains and are of a normal recurring nature. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2006 Annual Report on Form 10-K. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Refer to the Company’s 2006 Annual Report on Form 10-K for a complete discussion regarding White Mountains’ significant accounting policies.

Minority Interest

Minority interests consist of the ownership interests of noncontrolling shareholders in consolidated subsidiaries, and are presented separately on the balance sheet. The portion of income attributable to minority interests is presented net of related income taxes in the statement of income and comprehensive income. The change in unrealized investment gains, foreign currency translation and the change in the fair value of the interest rate swap to hedge OneBeacon’s exposure to variability in the interest rate on its mortgage note are presented in accumulated other comprehensive income net of the minority interest portion.  The percentage of the noncontrolling shareholders’ ownership interest in OneBeacon Ltd. at September 30, 2007 and December 31, 2006 was 28.1% and 27.6%.

White Mountains began to present minority interest subsequent to the OneBeacon Offering.  The portion of income attributable to minority interest in certain limited partnership investments has been reclassified to conform with the presentation of the minority interest in OneBeacon Ltd.

On May 24, 2007, White Mountains Re Group, Ltd. (“WMRe Group”), an intermediate holding company of White Mountains Re, issued $250 million non-cumulative perpetual preference shares (“the Preference Shares”) (See Note 2).  The Preference Shares and dividends thereon are included in minority interest on the balance sheet and as minority interest expense on the statement of income and comprehensive income, respectively.

Recently Adopted Changes in Accounting Principles

Federal, State and Foreign Income Taxes

While White Mountains is subject to taxation in several jurisdictions, the majority of White Mountains’ subsidiaries file consolidated tax returns in the United States.  Income earned or losses generated by companies outside the United States are generally subject to an overall effective tax rate lower than that imposed by the United States.

On January 1, 2007 White Mountains adopted FASB Interpretation No. 48, Accounting for Uncertainty in Income Taxes (“FIN 48”). FIN 48 prescribes when the impact of a given tax position should be recognized and how it should be measured.  Under the new guidance, recognition is based upon whether or not a company determines that it is more likely than not that a tax position will be sustained upon examination based upon the technical merits of the position. In evaluating the more-likely-than-not recognition threshold, White Mountains must presume that the tax position will be subject to examination by a taxing authority with full knowledge of all relevant information. If the recognition threshold is met, then the tax position is measured at the largest amount of benefit that is more than 50% likely of being realized upon ultimate settlement.

FIN 48 also addresses how interest and penalties should be accrued for uncertain tax positions, requiring that interest expense should be recognized in the first period interest would be accrued under the tax law. White Mountains classifies all interest and penalties on unrecognized tax benefits as part of income tax expense.  At January 1, 2007, White Mountains had accrued interest and penalties of $3.8 million, net of federal benefit. In connection with the adoption of FIN 48, White Mountains recognized a $.2 million decrease in the liability for unrecognized tax benefits, primarily as a result of reductions in its estimates of accrued interest. The effect of adoption has been recorded as an adjustment to opening retained earnings.

At January 1, 2007, White Mountains had $70.6 million of unrecognized tax benefits.  If recognized, $60.3 million would increase net income and reduce the effective tax rate.  The remaining $10.3 million of unrecognized tax benefits relate to tax positions for which ultimate deductibility is highly certain but the timing of deductibility is uncertain.  Recognition of these tax benefits, other than any applicable interest and penalties, would not affect the effective tax rate.  There have been no material changes to these balances since adoption.

With few exceptions, White Mountains is no longer subject to U.S. federal, state or non-U.S. income tax examinations by tax authorities for years before 2003.  The Internal Revenue Service (“IRS”) commenced an examination of White Mountains’ U.S. income tax returns for 2003 and 2004 in the second quarter of 2006 that is

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anticipated to be completed by the end of 2008. As of September 30, 2007, the IRS has not proposed any significant adjustments to taxable income.  White Mountains does not expect the IRS to propose any adjustments that would result in a material change to its financial position.

As of September 30, 2007, White Mountains does not anticipate any significant changes to its total unrecognized tax benefits within the next twelve months.

Recent Accounting Pronouncements

Fair Value Measurements

In September 2006, the FASB issued Statement of Financial Accounting Standards No. 157, Fair Value Measurements (“FAS 157”). The Statement provides a revised definition of fair value and guidance on the methods used to measure fair value. The Statement also expands financial statement disclosure requirements for fair value information. The Statement establishes a fair value hierarchy that distinguishes between assumptions based on market data from independent sources (“observable inputs”) and a reporting entity’s internal assumptions based upon the best information available when external market data is limited or unavailable (“unobservable inputs”). The fair value hierarchy in FAS 157 prioritizes inputs within three levels. Quoted prices in active markets have the highest priority (Level 1) followed by observable inputs other than quoted prices (Level 2) with unobservable inputs having the lowest priority (Level 3). The guidance in FAS 157 is applicable to derivatives as well as other financial instruments measured at fair value and nullifies the guidance that provided for the deferral of gains at the date of initial measurement. The Statement is effective for financial statements issued for fiscal years beginning after November 15, 2007.  White Mountains has not yet determined the effect of adoption on its financial condition, results of operations or cash flows.

Fair Value Option

In February 2007, the FASB issued Statement of Financial Accounting Standards No. 159, The Fair Value Option for Financial Assets and Financial Liabilities (“FAS 159”). The Statement allows companies to make an election, on an individual instrument basis, to report financial assets and liabilities at fair value. The election must be made at the inception of a transaction and may not be reversed. The election may also be made for existing financial assets and liabilities at the time of adoption. Unrealized gains and losses on assets or liabilities for which the fair value option has been elected are to be reported in earnings. The Statement requires additional disclosures for instruments for which the election has been made, including a description of management’s reasons for making the election. The Statement is effective as of fiscal years beginning after November 15, 2007 and is to be adopted prospectively and concurrently with the adoption of FAS 157. White Mountains has not yet determined the effect of adoption on its financial condition, results of operations or cash flows.

Note 2. Significant Transactions

Preference Shares

On May 24, 2007, WMRe Group issued 250,000 non-cumulative perpetual preference shares with a $1,000 per share liquidation preference. Proceeds of $245.7 million, net of $4.3 million of issuance costs and commissions, were received from the issuance. Holders of the Preference Shares receive dividends on a non-cumulative basis when and if declared by WMRe Group. The holders of the Preference Shares have the right to elect two directors to WMRe Group’s board in the event of non-payment of dividends for six quarterly dividend periods. The right ceases upon the payment of dividends for four quarterly periods or the redemption of the Preference Shares. In addition, WMRe Group may not declare or pay dividends on its common shares unless it is current on its most recent dividend period. The dividend rate is fixed at an annual rate of 7.506% until June 30, 2017. After June 30, 2017, the dividend rate will be paid at a floating annual rate, equal to the greater of 3 month LIBOR plus 3.20% or 7.506%. The Preference Shares are redeemable solely at the discretion of WMRe Group on or after June 30, 2017 at their liquidation preference, plus any declared but unpaid dividends. Prior to June 30, 2017, WMRe Group may elect to redeem the Preference Shares at an amount equal to the greater of 1) the aggregate liquidation preference of the shares to be redeemed and 2) the sum of the present values of the aggregate liquidation preference of the shares to be redeemed and the remaining scheduled dividend payments on the shares to be redeemed (excluding June 30, 2017), discounted to the redemption date on a semi-annual basis at a rate equal to the rate on a comparable treasury issue, plus 45 basis points.  In the event of liquidation of WMRe Group, the holders of the Preference Shares would have preference over the common shareholders and would receive a distribution equal to the liquidation preference per share, subject to availability of funds.

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Note 3.  Loss and Loss Adjustment Expense Reserves

The following table summarizes the loss and loss adjustment expense (“LAE”) reserve activities of White Mountains’ insurance subsidiaries for the three and nine months ended September 30, 2007 and 2006:

(1) During the three months ended September 30, 2007, White Mountains Re recorded a $9.0 million decrease on its workers compensation loss reserves relating to its Sierra Insurance Group acquisition, which was offset dollar-for-dollar by an increase in the principal amount of the Sierra Note that White Mountains Re issued as part of that acquisition (See Note 6).

White Mountains experienced $.9 million and $53.4 million of net favorable development on prior accident year loss reserves during the three and nine months ended September 30, 2007. For the three months ended September 30, 2007, OneBeacon had net favorable development of $16.5 million that was offset primarily by $15.0 million of net unfavorable development at Esurance.  For the nine months ended September 30, 2007, OneBeacon, White Mountains Re, and Other Operations had net favorable development of $41.2 million, $25.1 million and $10.5 million, respectively, offset by $23.4 million of net unfavorable development at Esurance.  OneBeacon’s net favorable development in 2007 that primarily related to professional liability and tuition reimbursement in specialty lines, property and general liability in commercial lines and automobile liability in traditional personal lines and at AutoOne. Esurance experienced net unfavorable development in 2007 that primarily related to bodily injury claims from prior accident years. Net favorable development at White Mountains Re in 2007 primarily related to property lines. The Other Operations segment experienced $10.5 million of favorable development during 2007 primarily due to the settlement of a large claim at British Insurance Company.

White Mountains experienced $28.9 million of net unfavorable development on prior accident year loss reserves during the three months ended September 30, 2006, primarily due to $9.4 million of adverse development at OneBeacon, which mostly related to prior year catastrophe losses, and $12.0 million of adverse development at Folksamerica Re on business assumed through a prior acquisition.  White Mountains experienced $233.8 million of net unfavorable development on prior accident year loss reserves during the nine months ended September 30, 2006, which in addition to the items listed above, primarily related to hurricanes Katrina, Rita and Wilma.

In connection with purchase accounting for the acquisitions of OneBeacon, Sirius International and Stockbridge Insurance Company, White Mountains was required to adjust loss and LAE reserves and the related reinsurance recoverables to fair value on their respective acquired balance sheets.  The net reduction to loss and LAE reserves is being recognized through an income statement charge ratably with and over the period the claims are settled. Accordingly, White Mountains recognized $5.4 million and $16.0 million of such charges for the three and nine months ended September 30, 2007, respectively, and $6.6 million and $18.2 million of such charges for the three and nine months ended September 30, 2006, respectively.

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Note 4. Third Party Reinsurance

In the normal course of business, White Mountains’ insurance and reinsurance subsidiaries may seek to limit losses that may arise from catastrophes or other events by reinsuring with third party reinsurers. White Mountains remains liable for risks reinsured in the event that the reinsurer does not honor its obligations under reinsurance contracts.

OneBeacon

At September 30, 2007, OneBeacon had $20.6 million of reinsurance recoverables on paid losses and $2,924.7 million (gross of $225.1 million in purchase accounting adjustments) that will become recoverable if claims are paid in accordance with current reserve estimates. The collectibility of balances due from OneBeacon’s reinsurers is critical to OneBeacon’s financial strength because reinsurance contracts do not relieve OneBeacon of its primary obligation to its policyholders. OneBeacon is selective with its reinsurers, placing reinsurance with only those reinsurers having a strong financial condition. OneBeacon monitors the financial strength of its reinsurers on an ongoing basis. As a result, uncollectible amounts have historically not been significant. The following table provides a listing of OneBeacon’s top reinsurers, excluding industry pools and associations, based upon recoverable amounts, the percentage of total reinsurance recoverables and the reinsurer’s A.M. Best rating.

(1)        A.M. Best ratings as detailed above are: “A++” (Superior, which is the highest of fifteen ratings), “A+” (Superior, which is the second highest of fifteen ratings) and “A” (Excellent, which is the third highest of fifteen ratings).

(2)        Includes $404.0 million of Third Party Recoverables, which NICO would pay under the terms of the NICO Cover (as defined below) if they are unable to collect from third party reinsurers. OneBeacon also has an additional $339.7 million of Third Party Recoverables from various reinsurers, the majority of which are rated “A” or better by A.M. Best.

(3)        At September 30, 2007, OneBeacon had assumed balances payable and expenses payable of approximately $24.0 million under its renewal rights agreement with Liberty Mutual Insurance Group (“Liberty Mutual”), which expired on October 31, 2003.

In connection with the OneBeacon Acquisition, the seller caused OneBeacon to purchase two reinsurance contracts: a full risk-transfer cover from National Indemnity Company (“NICO”) for up to $2.5 billion in old asbestos and environmental (“A&E”) claims and certain other exposures (the “NICO Cover”) and an adverse development cover (the “GRC Cover”) from General Reinsurance Corporation (“GRC”) for up to $570.0 million, comprised of $400.0 million of adverse development on losses occurring in years 2000 and prior in addition to $170.0 million of reserves ceded as of the date of the OneBeacon Acquisition. The NICO Cover and GRC Cover, which were contingent on and occurred contemporaneously with the OneBeacon Acquisition, were put in place in lieu of a seller guarantee of loss and LAE reserves and are therefore accounted for as a seller guarantee under GAAP in accordance with Emerging Issues Task Force Technical Matter Document No. D-54 (“EITF Topic D-54”). NICO and GRC are wholly-owned subsidiaries of Berkshire Hathaway Inc. (“Berkshire”).

Under the terms of the NICO Cover, NICO receives the economic benefit of reinsurance recoverables (“Third Party Recoverables”) from certain of OneBeacon’s third party reinsurers in existence at the time the NICO Cover was executed. As a result, the Third Party Recoverables serve to protect the $2.5 billion limit of NICO coverage for the benefit of OneBeacon. White Mountains estimates that on an incurred basis, net of Third Party Recoverables, as of September 30, 2007 it has used approximately $2.1 billion of the coverage provided by NICO.  Approximately $952.6 million of these incurred losses have been paid by NICO through September 30, 2007. Since entering into the NICO Cover, $39.8 million of the $2.1 billion of utilized coverage from NICO related to uncollectible Third Party Recoverables. To the extent that actual experience differs from White Mountains’ estimate of ultimate A&E losses and Third Party Recoverables, future losses could utilize some or all of the protection remaining under the NICO Cover.

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Pursuant to the GRC Cover, OneBeacon is not entitled to recover losses to the full contract limit if such losses are reimbursed by GRC more quickly than anticipated at the time the contract was signed. OneBeacon intends to only seek reimbursement from GRC for claims which result in payment patterns similar to those supporting its recoverables recorded pursuant to the GRC Cover. The economic cost of not submitting certain other eligible claims to GRC is primarily the investment spread between the rate credited by GRC and the rate achieved by OneBeacon on its own investments. This cost, if any, is expected to be small.

Effective, July 1, 2007, OneBeacon renewed its property catastrophe reinsurance program through June 30, 2008.  The program provides coverage for all OneBeacon property business including automobile physical damage, as well as terrorism coverage for non-TRIA events (excluding nuclear, biological, chemical and radiological).  Under the program, the first $150 million of losses resulting from a single catastrophe are retained by OneBeacon and $650 million of the next $700 million of losses resulting from the catastrophe are reinsured.  Any loss above $850 million would be retained by OneBeacon. In the event of a catastrophe, OneBeacon’s property catastrophe reinsurance program is reinstated for the remainder of the original contract term by paying a reinstatement premium that is based on the percentage of coverage reinstated and the original property catastrophe coverage premium.

White Mountains Re

White Mountains Re’s principal reinsurance protection at September 30, 2007 is provided through Folksamerica Re’s quota share retrocessional arrangements with Olympus Reinsurance Company Ltd. (“Olympus”) and Helicon Reinsurance Company, Ltd. (“Helicon”) and through excess of loss protection purchased by Sirius International to cover Sirius International’s property catastrophe and aviation exposures. Folksamerica Re has notified Olympus and Helicon that it will not renew the quota share arrangements for 2008.

At September 30, 2007, White Mountains Re had $35.8 million of reinsurance recoverables on paid losses and $851.5 million that will become recoverable if claims are paid in accordance with current reserve estimates. Because reinsurance contracts do not relieve White Mountains Re of its obligation to its ceding companies, the collectibility of balances due from its reinsurers is critical to White Mountains Re’s financial strength. White Mountains Re monitors the financial strength of its reinsurers on an ongoing basis. The following table provides a listing of White Mountains Re’s top reinsurers based upon recoverable amounts, the percentage of total recoverables and the reinsurers’ A.M. Best ratings.

(1)        Non-U.S. insurance entities. Balances are fully collateralized through funds held, letters of credit or trust agreements.

(2)        A.M. Best ratings as detailed above are: “NR-4” (Not rated per company request), “A++” (Superior, which is the highest of fifteen ratings), “A+” ( Superior, which is the second highest of fifteen ratings), “A” (Excellent, which is the third highest of fifteen ratings), and “A-” (Excellent, which is the fourth highest of fifteen ratings).

(3)        Gross of $137.0 million due to Olympus under an indemnity agreement with Folksamerica Holdings.

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Note 5.  Investment Securities

White Mountains’ invested assets comprise securities and other investments held for general investment purposes and those held in a segregated trust account established in connection with the OneBeacon Offering to economically defease the Berkshire Preferred Stock and the Zenith Preferred Stock.

White Mountains’ portfolio of fixed maturity investments and common equity securities, excluding convertible bonds, held for general investment purposes is classified as available for sale and is reported at fair value as of the balance sheet date as determined by quoted market prices.  Net unrealized investment gains and losses on available for sale securities are reported net, after-tax, as a separate component of shareholders’ equity.  Changes in net unrealized investment gains and losses, net of the effect of adjustments for minority interest and after-tax, are reported as a component of other comprehensive income.

White Mountains has elected the fair value option for its investment in convertible bonds.  Convertible bonds are carried at fair value with changes in value recorded in income as realized investment gains.

White Mountains has invested in mortgage backed and asset-backed securities, which are classified as available for sale and carried at fair value within fixed maturity investments.  Fair values are based on quoted market prices from a third party pricing service. Income on mortgage-backed and asset-backed securities is recognized using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When actual prepayments differ significantly from anticipated prepayments, the estimated economic life is recalculated and the remaining unamortized premium or discount is amortized prospectively over the remaining economic life.

The portfolio of fixed maturity investments held in the segregated trust account are classified as held to maturity as White Mountains has the ability and intent to hold the investments until maturity. Securities classified as held to maturity are recorded at amortized cost.

Investment securities are regularly reviewed for impairment based on criteria that include the extent to which cost exceeds market value, the duration of the market decline, the financial health of and specific prospects for the issuer and the ability and intent to hold the investment to recovery.  Investment losses that are other than temporary are recognized in earnings.  Realized gains and losses resulting from sales of investment securities are accounted for using the weighted average method.  Premiums and discounts on all fixed maturity investments are accreted to income over the anticipated life of the investment.  Short-term investments consist of money market funds, certificates of deposit and other securities which mature or become available for use within one year.  Short-term investments are carried at amortized cost, which approximated fair value as of September 30, 2007 and December 31, 2006. Short-term investments held in the segregated trust account are included in the total of investments held in trust.

Other investments comprise White Mountains’ investments in limited partnerships, warrants, equity method investments and an interest rate swap accounted for as a cash flow hedge.

Net investment income for the three and nine months ended September 30, 2007 and 2006 consisted of the following:

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Realized investment gains (losses) consisted of the following: