Exhibit 10.18

ONEBEACON
DEFERRED COMPENSATION PLAN

ARTICLE I

Purpose

SECTION 1.01.                                            Purpose .  The purpose of this Plan is to provide Key Employees with the ability to defer the receipt of Compensation.  The Plan is also intended to establish a method of attracting and retaining persons whose abilities, experience and judgment can contribute to the long-term strategic objectives of the Company.

SECTION 1.02.                                            Unfunded Plan .  The Company intends that the Plan be an unfunded non-qualified deferred compensation plan maintained primarily for the purpose of providing deferred benefits for a select group of management or highly compensated service providers of the Company and its subsidiaries.

ARTICLE II

Definitions

The following terms when used in this Plan have the designated meanings unless a different meaning is clearly required by the context.

SECTION 2.01.                                            “ Account ” means the records maintained on the books of the Company to reflect deferrals of Compensation by a Participant pursuant to Section 3.03.

SECTION 2.02.                                            “ Administrator ” means the person or committee designated by the Committee as responsible for the day-to-day administration of the Plan.

SECTION 2.03.                                            “ Beneficiary ” means the person or persons designated pursuant to Article 5 to receive a benefit pursuant to Section 4.04(a) in the event of a Participant’s death before his benefit under this Plan has been paid.

SECTION 2.04.              “ Board ” means the Board of Directors of the Company.

SECTION 2.05.              “ Change in Control ” means a “Change in Control” as defined in the White Mountains Long-Term Incentive Plan.

SECTION 2.06.                                            “ Committee ” means the OneBeacon Benefits Committee; provided that any determination involving a Participant who is a member of the Committee shall be made by the Board.

SECTION 2.07.                                            “ Company ” means OneBeacon Insurance Company and any successor thereto.

SECTION 2.08.                                            “ Compensation ” means, for any Plan Year, (i) the base salary to be paid to an eligible employee for such Plan Year, the annual bonus, if any, to be

paid to an eligible employee in such Plan Year, the long-term incentive compensation, if any, to be paid to an eligible employee in such Plan Year or any other compensation to be paid to an eligible employee during that Plan Year that is designated as “Compensation” hereunder by the Administrator or (ii) any fee or other compensation to be paid to an eligible consultant by the Company or its subsidiaries for such Plan Year that it is designated as “Compensation” hereunder by the Administrator.

SECTION 2.09.                                            “ Fiscal Year ” means the calendar year.

SECTION 2.10.                                            “ Fund ” means any investment fund selected by the Administrator to be offered under the Plan.

SECTION 2.11.                                            “ Key Employee ” means any executive employee, other overtime-exempt employee or consultant of the Company or its participating subsidiaries who the Administrator, in its sole discretion, decides is important to the ongoing business objectives of the Company.

SECTION 2.12.                                            “ Market Price ” on any day means (i) if Shares are listed on the New York Stock Exchange, the average of the high and low sales price, or, in case no such sale takes place on such day, the average of the last quoted closing bid and asked prices, regular way, in either case as reported in the principal consolidated transaction reporting system with respect to securities listed or admitted to trading on the New York Stock Exchange or, if Shares are not listed or admitted to trading on the New York Stock Exchange, as reported in the principal consolidated transaction reporting system with respect to securities listed on the principal national securities exchange on which Shares are listed or admitted to trading or, if Shares are not listed or admitted to trading on any national securities exchange, the last quoted sale price or, if not so quoted, the average of the high bid and the low asked prices in the over-the-counter market, as reported by NASDAQ or such other system then in use, or, if on any such date Shares are not quoted by any such organization, the average of the closing bid and asked prices as furnished by one or more professional market makers making a market in Shares and (ii) if Shares are not publicly held or so listed or publicly traded, the fully diluted book value per Share as determined by the Administrator in accordance with United States generally accepted accounting principles.

SECTION 2.13.                                            “ Participant ” means a Key Employee who has deferred Compensation pursuant to this Plan and who has an Account to which amounts stand credited.

SECTION 2.14.                                            “ Payment Period ” means the month and year designated pursuant to Section 3.04 for payment of some portion or all of a Participant’s Account.

SECTION 2.15.                                            “ Plan ” means this “OneBeacon Deferred Compensation Plan” as set forth herein and as amended from time to time.

SECTION 2.16.                                            “ Plan Year ” means the calendar year.

SECTION 2.17.                                            “ Share(s) ” means a common share(s) of White Mountains Insurance Group, Ltd., par value $1.00.

SECTION 2.18.                                            “ Termination of Service ” means, as applicable, cessation for any reason of a Key Employee’s (i) service as an employee of the Company and its

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subsidiaries or (ii) status as a consultant to the Company and its subsidiaries as determined by the Committee in its sole discretion.

SECTION 2.19.                                            “ Valuation Date ” means the date that the Administrator makes a valuation of an Account.  Unless otherwise provided by the Administrator, each deemed investment alternative within each Account shall be valued as of each day on which a value for such deemed investment alternative reasonably is available to the Administrator.

ARTICLE III

Eligibility and Deferrals

SECTION 3.01.                                            Eligibility .  Each Key Employee designated by the Administrator as eligible to participate in the Plan shall be eligible to be a Participant hereunder.  The Administrator has the sole and complete discretion to determine which Key Employees are eligible to participate on a Plan Year by Plan Year basis.  No Key Employee shall have a right to be designated as a Participant and the designation of a Key Employee as a Participant in one Plan Year shall not obligate the Administrator to continue such Key Employee as a Participant in subsequent Plan Years.

SECTION 3.02.                                            Accounts.   The Administrator shall establish an Account for each Key Employee who elects to defer Compensation pursuant to Section 3.03. Amounts deferred pursuant to Section 3.03, and the value thereof determined pursuant to Section 3.05, shall be credited to such Account.

SECTION 3.03.                                            Deferral of Compensation.   A Key Employee may elect to reduce the Compensation otherwise payable to him during a Plan Year and to have such amount credited to his Account.  A deferral direction pursuant to this Section 3.03 shall be made in writing at such time and in such manner as the Administrator shall prescribe but must in any event be made before the first day of the Plan Year in which such Compensation would otherwise be paid.  A deferral election shall apply only with respect to the Plan Year for which it is made and shall not continue in effect for any subsequent Plan Year.  A deferral election, once executed and filed with the Administrator, cannot be revoked after the date specified by the Administrator.  Notwithstanding the foregoing, (i) any Key Employee who is first hired by the Company or a participating subsidiary during a Plan Year may elect within 30 days after becoming a Key Employee to defer any unpaid portion of his Compensation in respect of such Plan Year and (ii) Key Employees may elect to defer any unpaid Compensation for the Plan Year in which this Plan is first adopted by the Board.

SECTION 3.04.                                            Payment Period.   (a)  Designation .  Each deferral direction given pursuant to Section 3.03 shall include designation of the Payment Period for the value of the amount deferred, subject to the limitation set forth in Section 3.04(c).

(b)                                  Adjustment.   The Committee may permit a Participant to irrevocably elect, no later than one year before the first day of the Payment Period initially designated pursuant to Section 3.04(a), to adjust such Payment Period, subject to the limitation set forth in Section 3.04(c).

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(c)                                   Limitation.   A Participant may select a Payment Period (or adjusted Payment Period) that begins no sooner than the first anniversary of the date of such election.

(d)                                  Methods of Payments.   A Participant may elect, at the time a Payment Period is selected, to receive the amount which will become payable as of such Payment Period in no more than 10 annual installments.  Except as may be elected pursuant to this Section 3.04(d), all amounts becoming payable under this Plan shall be paid in a single payment.

(e)                                   Irrevocability.   Except as provided in Section 3.04(b) or as set forth in Article IV, a designation of a Payment Period and an election of installment payments shall be irrevocable; provided , however , that payment may be made at a different time as provided in Section 4.04.

SECTION 3.05.                                            Value of Participants’ Accounts.   Compensation deferrals shall be allocated to each Participant’s Account on the first business day following the date such Compensation is withheld from the Participant’s Compensation and shall be deemed invested pursuant to this Section 3.05, as soon as practicable thereafter.

(a)                                   Crediting of Income, Gains and Losses.   As of each Valuation Date, income, gain and loss equivalents (determined as if the Account is invested in the manner set forth below) attributable to the period following the next preceding Valuation Date shall be credited to and/or deducted from the Account.

(b)                                  Investment of Account Balance.   The Participant may select, from various Funds made available hereunder, the Funds in which all or part of his Account shall be deemed to be invested.

(i)                The Participant shall make an investment designation on a form provided by the Administrator, which shall remain effective until another valid designation has been made by the Participant as herein provided.  The Participant may amend his investment designation by giving written direction to the Administrator in accordance with procedures established by the Administrator.  A timely change to a Participant’s investment designation shall become effective on the date determined under the applicable procedures established by the Administrator.

(ii)             Any changes to the Funds to be made available to the Participant, and any limitation on the maximum or minimum percentages of the Participant’s Account that may be invested in any particular medium, shall be communicated from time to time to the Participant by the Administrator.

(c)                                   Default Provision.   Except as provided below, the Participant’s Account shall be deemed to be invested in accordance with his investment designations, provided such designations conform to the provisions of this Section.  Notwithstanding the above, the Committee, in its sole discretion, may disregard the Participant’s election and determine that all Compensation deferrals shall be deemed to be invested in a Fund determined by the Committee.  In the event that any Fund under which any portion of the Participant’s Account is deemed to be invested ceases to exist, such portion of the Account thereafter shall be deemed held in the Fund selected by the Participant or, in the absence of any instructions from the Participant, by the Committee, subject to subsequent deemed investment elections.

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(d)                                  Statements.   The Company shall provide an annual statement to the Participant showing such information as is appropriate, including the aggregate amount credited to the Account, as of a reasonably current date.

SECTION 3.06.                                            Limit on Account Balance.   Notwithstanding anything to the contrary contained herein, the maximum aggregate amount that may be credited to a Participant’s Account (including, without limitation, Compensation deferrals and investment gains thereon) as of any Valuation Date shall be $50,000,000 or such other amount as may be designated by the Committee.  Any amount credited to a Participant’s Account in excess of the applicable limit hereunder shall be promptly distributed to the Participant in (as determined by the Committee) cash or Shares