**Exhibit 4.51****Standard Stock Option Plan****of Converium Holding AG, Zug, Switzerland**December 2006**1** **Introduction** 1.1 The Converium Stock Option Plan (the “**Plan**”) is an incentive scheme of Converium HoldingAG, Zug, Switzerland (the “**Company**”). 1.2 The Plan shall provide an increased incentive for selected employees and members of the boardof directors (the “**Board of Directors**”) of the Company and of its subsidiaries to contributeto the future success and prosperity of the Company, which will enhance the value of the stockof the Company for the benefit of the Company’s shareholders and increase the ability of theCompany to attract and retain employees of exceptional skill and experience. 1.3 The Plan shall provide these employees and members of the Board of Directors an opportunityto obtain options to acquire shares of the Company (the “**Shares**”). An option shall mean aright granted under this Plan to purchase one Share (the “**Option(s)**”). The Options will be issued by the Company. 1.4 All rights and obligations of the participant(s) in the Plan (the “**Participant(s)**”) are asdescribed in these terms and conditions of the Plan. **2** **Participation in the Plan** 2.1 Eligible Participants of this Plan are generally selected executive staff and other keypersonal as well as members of the Board of Directors. Participants will be determined by theNomination and Remuneration Committee of the Board of Directors (the “**Committee**”) and/or other bodies of the Converium group. 2.2 The holding of one of the positions mentioned in clause 2.1 shall grant no right toparticipate or to a continued participation in the Plan or to employment with the Company or asubsidiary of the Company. The Committee shall have full discretion to elect persons otherthan those mentioned in clause 2.1 as Participants.Standard Stock Option Plan rev. December 20061/6
 

 
**3** **Grant of Options** 3.1 Options are granted to Participants free of charge, subject to any payments made on 3.2 account of social insurance, pension fund or similar contributions or other payments ordeductions to be made by an employer on salary payments in general which payments ordeductions will be shared between the Participant and the Company (or other employer of theParticipant) on the same basis as ordinary salary payments of Participants of the relevantemployer (or fees of members of the Board of Directors). 3.3 Depending on the Plan, Option grants are scheduled to take place once or twice a year. Thetime of the grant of Options and the number of Options granted to a Participant will bedetermined by the Committee and/or other bodies of the Converium group and communicated toeach Participant in the form of a grant notice (the “**Grant Notice**”). The Grant Notice shallalso set forth the other terms and conditions of the Options which are not specified in thisPlan. In the event of any discrepancy between the terms and conditions of the Grant Notice andthose of this Plan, the terms and conditions of the Grant Notice shall prevail. **4** **Strike Price of Options**   The strike price of a particular Option is the price at which one Share may bepurchased under the Option (the “**Strike Price**”). The Strike Price will be as set forth inthe Grant Notice and shall in general correspond to the closing price of the Shares on theSWX Swiss Exchange on or about the date of the Grant Notice or the closing price of theShares on the SWX Swiss Exchange on the beginning and/or end of the respective grantperiod. **5** **Exercise of Options** 5.1 Subject to Section 7, Options may be exercised in one or more installments at any timeafter the expiry of the applicable vesting period until the expiration of the Options asstated in the relevant Grant Notice. 5.2 In order to exercise Options, Participants will have to complete and send to the planadministrator appointed by the Committee (the “**Plan Administrator**”) an exercise notice (the“**Exercise Notice**”). Upon receipt of the duly completed exercise notice by the PlanAdministrator, the exercise of the respective Options will become binding on and irrevocableby the Participant. 5.3 Unless provided for differently in the Grant Notice, the Participant shall, at the time ofsending the exercise notice, transfer the Strike Price applicable to the Options exercised tothe bank account indicated in theExercise Notice. If the exercise of the Options and/or the delivery of the Shares is, atthe time of exercise, subject to stamp duty,Standard Stock Option Plan rev. December 20062/6
 

 
  similar tax or levy, the Participant shall, simultaneously with the transfer of theStrike Price, also transfer the amount necessary to pay such stamp duty, similar tax orlevy. The Plan Administrator will inform the Participants from time to time accordingly. **6** **Delivery of Shares** 6.1 The Shares will be delivered as soon as possible after receipt by the Plan Administratorof the Exercise Notice and with all rights (such as dividend rights) pertaining to such Shareson the date of delivery. Delivery of the Shares on that date is conditional upon receipt bythe Plan Administrator of a duly completed Exercise Notice and the Strike Price applicable tothe Options exercised (as well as stamp duty, similar tax or levy, if any). 6.2 The Shares will be delivered to the securities account of the Participant opened with thePlan Administrator or its correspondent bank. **7** **Vesting Period** 7.1 The right to the Options is conditional upon the Participant being an Employee (asdefined below) on the dates specified in the Grant Notice under “Vesting”:   For the purposes of this Section 7, the expression “**Employee**” shall mean a Participantwho is employed (and who is not an employee with an hourly wage) by the Company, a companydirectly or indirectly controlled by the Company (or any other company or business asdetermined by the Committee in its absolute discretion), provided, however, that on therelevant date, no notice of termination has been given or termination agreement concludedin respect of the employment agreement of such Employee, other than as provided for inSection 7.2.3. A transfer of an Employee from the Company or an affiliated company to theCompany or another affiliated company, and a leave of absence, duly authorized in writingby the relevant employer, for military service or sickness, or for any other purposeapproved by the Committee shall not be deemed a termination of employment unlessemployment is terminated during such leave of absence. 7.2 Disregarding the provisions of Section 7.1, the right of a Participant to the Options shallbecome unconditional at the time one of the following events occurs: 7.2.1 Normal retirement of the Participant;  7.2.2 permanent disability of the Participant, as determined by the Company;  7.2.3 death of the Participant;  7.2.4 termination of employment based on grounds for which the employer of theParticipant, the Company and/or any of its subsidiaries are solely responsible;  7.2.5 transfer of a Participant from the Company or an affiliated company to theCompany or another affiliated company in another tax jurisdiction, if theStandard Stock Option Plan rev. December 20063/6
 

 
     Committee decides, in its sole discretion, that the right of a Participantto the Options shall become unconditional.  1If a Participant ceases to be an Employee for any reason other than those setout in Section 7.2.1 and 7.2.2, the Options held by such Participant or its successors maybe only exercised within three months after such event (one year in case of death) and notlater than their expiration date as stated in the relevant Grant Notice. Options notexercised during this three months period (one year in case of death) shall lapse. **8** **Adjustment of the Plan and of Options** 8.1 In the event of a Potential Adjustment Event (as defined below), the Board of Directorsof the Company shall, if deemed necessary by the Board of Directors, adjust the rights underthe Plan and the Options outstanding, by applying adjustment methods customary in the marketat that time. For the purposes hereof, a “**Potential Adjustment Event**” includes: 8.1.1 a sub-division, consolidation or reclassification of the Shares;  8.1.2 a grant or distribution to existing holders of Shares of subscription orother rights for the acquisition of Shares or other securities or rights granting theright to payment of dividends and/or the proceeds of liquidation of the Company, inany case for free or for payment (cash or other) at less than the prevailing marketprice as determined by the Committee;  8.1.3 a reduction of the share capital or of other securities or rights grantingthe right to payment of dividends and/or the proceeds of liquidation of the Company(in any case by way of a cancellation of Shares or such other securities or rights);  8.1.4 any similar event that may have a diluting or concentrative effect on themarket value of the Shares;  8.1.5 a consolidation, amalgamation or merger of the Company, in which theCompany is not the continuing corporation;  8.1.6 a sale by the Company of all or substantially all of its business and / orassets to a person or entity which is not a wholly-owned subsidiary of the Company;8.2 In the event of a Potential Adjustment Event, the Board of Directors shall also have theright to decide that Options shall vest or to terminate the Plan and buy back or canceloutstanding Options against such cash or other compensation to the Participants as the Boardof Directors shall determine in its sole discretion.8.3 Any Additional Taxes (as defined below) that may be imposed on the Participant as a 1 amended August 23, 2003Standard Stock Option Plan rev. December 20064/6
 

 
  result of such a modification of the terms and conditions of the Options or of thePlan and/or, following such modification, an exercise of Options, shall be borne by theCompany. In this context, “**Additional Taxes**” means such taxes, social contributions andsimilar duties in excess of those which would have been borne by the Participant absentsuch a modification of the terms and conditions of the Options. **9** **Take-over situation****1**Upon the occurrence of a Take-over Situation (as defined below) all outstanding Optionsgranted shall immediately vest. For the purposes hereof, a “Take-over Situation” shall mean theconclusion of a binding tender offer for more than 33 1/3 per cent of the total voting power(whether exercisable or not) of the Company by a person (or two or more persons acting in concert),provided that the conditions, if any, for such offer have been met or waived.**10** **Taxes / Social Security / Brokerage Fees** 10.1 All taxes, duties and similar charges imposed or levied in connection with the exerciseof Options and the holding and transfer of Shares, such as stamp duties, value added taxes,direct taxes of the Participant (excluding direct taxes imposed on the Company or the relevantemployer), will be payable by the Participant. 10.2 Unless provided for differently in the Grant Notice, all payments on account of socialinsurance, pension fund or similar contributions to be made in connection with the exercise ofOptions, the holding of Shares as a result of such exercise and the transfer or disposal ofShares acquired through the exercise of Options will be payable by the Participant. 10.3 All brokerage fees charged by the Plan Administrator in connection with the exercise ofOptions and the transfer of the Shares resulting from such exercise to the account of theParticipant with the Plan Administrator or its correspondent bank will be borne by theCompany. Brokerage fees and costs and expenses related to a later transfer or sale of suchShares will be borne by the Participant. **11** **Transfer Restriction / Forfeiture** 11.1 The Options granted under the Plan may not be transferred or pledged by theParticipant, except that the Board of Directors, in its absolute discretion, may permit atransfer or pledge thereof, which transfer or pledge shall become effective only uponregistration thereof in the relevant register. 11.2 Grant Notices may provide for immediate forfeiture of an Option, or Shares acquired uponexercise of an Option, or clawback of any gain realized thereon, in the event that 1 inserted April 20, 2004/amended by NRC on November 29, 2006Standard Stock Option Plan rev. December 20065/6
 

 
  the relevant Participant engages in activities inimical to the interests of theCompany and/or any of its subsidiaries, as determined by the Committee. **12** **No Segregation**   The Company will not and shall not be required to segregate any Shares or any cashwhich may at any time be represented by the Options and the Plan shall constitute anunfunded plan of the Company. **13** **Amendment and Administration of the Plan** 13.1 The Board of Directors shall have the right to amend or terminate the Plan or to decideon modifications thereof in a particular case at any time. On termination, the Plan remainsapplicable to Options outstanding at that time unless such Options are terminated by the Boardof Directors at the same time. 13.2 Unless provided for differently in this Plan, decisions with respect to this Plan shall betaken by the Committee who shall delegate administrative functions to the Plan Administrator. 13.3 The Plan Administrator shall administer the Plan and maintain a register setting out, interalia, the details of each Participant and the number of vested and unvested Options to whichsuch Participant is entitled to, showing their vesting date and expiration date and StrikePrice. 13.4 The Plan Administrator shall establish rules and regulations for the administration of thePlan, in particular the exercise of Options, the allotment of Shares and the sale or transferof Shares. **14** **Applicable law / jurisdiction** 14.1 **The Plan and the rights granted thereunder shall be subject to and governed by Swisslaw.** 14.2 **Exclusive place of jurisdiction for all disputes arising out of or in connection with thisPlan shall, to the extent legally possible, be the commercial courts of Zurich, Switzerland.** **15** **Acceptance of the Plan**   **By accepting any Option or any related right, the Participant explicitly acceptsthe terms and conditions of the Plan, in particular the choice of law and jurisdictionclause.**Standard Stock Option Plan rev. December 20066/6