Document:

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                                                                   EXHIBIT 10.18

                       QUOTA SHARE RETROCESSION AGREEMENT

                                 BY AND BETWEEN

                      PLATINUM UNDERWRITERS BERMUDA, LTD.

                                      and

                            PLATINUM RE (UK) LIMITED

                           DATED AS OF 27 MARCH, 2003

         This Quota Share Retrocession Agreement (this "Agreement"), is made by
and between Platinum Underwriters Bermuda, Ltd., a Bermuda-domiciled insurance
company (the "Retrocessionaire"), and Platinum Re (UK) Limited, a United
Kingdom-domiciled insurance company (the "Retrocedant").

ARTICLE 1 - BUSINESS COVERED

Retrocedant hereby obligates itself to retrocede to the Retrocessionaire and the
Retrocessionaire hereby obligates itself to accept a fifty-five percent (55%)
quota share of the reinsurance and retrocession contracts underwritten by
Retrocedant on or after the Effective Date (the "Reinsurance Contracts").

ARTICLE 2 -COMMENCEMENT AND TERMINATION

Subject to Article 14 (Security), this Agreement shall take effect and shall
apply to all Reinsurance Contracts underwritten on or after 12:01 a.m. London
time on the day following receipt by Retrocedant of permission from the
Financial Services Authority under Part IV of the Financial Services and Markets
Act 2000 to conduct reinsurance business in the United Kingdom (the "Effective
Date"). It shall remain continuously in force but may be terminated by either
party giving at least 90 days notice in writing to the other party or by
Retrocedent in accordance with Article 14 (Security). Such Notice of
cancellation shall apply in respect of the next succeeding year of account.

For the purposes of this agreement, each year of account shall apply to business
attaching or resigned during the period commencing with the 1st January and
ending with the following 31st December of each calendar year. Unless the
Retrocedant elects to reassume the ceded unearned premium in force on the
effective date of termination, and so notifies the Retrocessionaire, the
Retrocessionaire shall remain liable hereunder for its pro rata share of the
Retrocedant's liability under the Reinsurance Contracts until the expiration,
cancellation or termination of all of the Retrocedant's liabilities under the
Reinsurance Contracts.

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ARTICLE 3 - ORIGINAL CONDITIONS

All retrocessions assumed under this Agreement shall be subject to the same
rates, terms, conditions, waivers and interpretations, and to the same
modifications and alterations, as the respective Reinsurance Contracts.

This Agreement is solely between the Retrocedant and the Retrocessionaire, and
in no instance shall any other party have any rights under this Agreement except
as expressly provided otherwise in the Insolvency Article.

ARTICLE 4 - PREMIUMS AND COMMISSION

As premium for the reinsurance provided hereunder, the Retrocedant shall
retrocede to the Retrocessionaire fifty-five percent (55%) of the net premium
ceded to the Retrocedant under the Reinsurance Contracts. Net Premium is defined
as Gross Premium ceded to the Retrocedant under the Reinsurance Contracts less:
(1) return premiums, (2) applicable ceding and other commissions, (3) brokerage,
(4) ceded reinsurance premium, (5) taxes, and (6) other expenses associated with
underwriting.

Other expenses associated with underwriting shall be limited to a maximum of 10
percent (10%) of the Gross Premium ceded to the Retrocedant under the
Reinsurance Contracts.

Gross Premium is defined as the total sum of all premiums associated with
Reinsurance Contracts ceded to the Retrocedant, before any deductions.

ARTICLE 5 - TERRITORY

Coverage applies within the territorial limits of the Reinsurance Contracts
covered hereunder.

ARTICLE 6 - INURING REINSURANCE

It is understood and agreed that when the Retrocedant warrants that it is in the
best interest of the Retrocedant and the Retrocessionaire, Retrocedant may
purchase facultative reinsurance and any other treaty reinsurance. The premium
for said inuring reinsurance that inures to the benefit of the Retrocessionaire
will be deducted from the premium hereunder. All reinsurance purchased by the
Retrocedant inures to the benefit of the Retrocessionaire unless specifically
noted in Addendum A.

ARTICLE 7 -LOSS AND LOSS EXPENSE

The Retrocessionaire shall be liable for fifty-five percent (55%) of all loss,
loss adjustment expenses and other payment obligations as incurred by
Retrocedant under the Reinsurance Contracts on and after the Effective Date.

ARTICLE 8 - REPORTS AND REMITTANCES

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The retrocedant shall render separately, quarterly statements of account, in
arrears, in respect of each year of account, showing the total of all premiums,
written, paid loss and loss adjustment expenses, allowances, commissions, and
underwriting expenses relevant to that quarter. Such accounts shall be rendered,
as soon as possible after the close of the relevant quarter with the balance
payable within 45 days after the end of the respective quarter.

The retrocedant shall normally debit the retrocessionaire with their
proportionate share of paid losses and loss adjustment expenses in the quarterly
accounts rendered. The retrocedant may, however, at their discretion, request
the retrocessionaire to make immediate payment for their proportion of any
settled loss in excess of (pound)2 million for any one loss relating to this
agreement; provided that the retrocessionaire shall have the right to deduct
from any such payment any sums due to the retrocessionaire under this agreement
for any agreement renewing or replacing this agreement.

In addition, the Retrocedant will furnish the Retrocessionaire a quarterly
statement showing the unearned premium, the total reserves for outstanding
losses including loss adjustment expense, a breakdown for paid and outstanding
catastrophe losses and loss adjustment expense, and such other information as
may be required by the Retrocessionaire for completion of its annual statements
or other filings.

ARTICLE 9 - ACCESS TO RECORDS

The Retrocessionaire and its designated representatives shall have free access
at any reasonable time to all records of the Retrocedant which pertain in any
way to this Agreement.

ARTICLE 10 - ARBITRATION

All disputes and differences arising under or in connection with this Agreement
shall be referred to arbitration under the Arbitration Rules of the A.I.D.A.
Reinsurance and Insurance Arbitration Society of the UK ("ARIAS (UK)").

The Arbitration Tribunal shall consist of three arbitrators, one to be appointed
by the Claimant, one to be appointed by the Respondent and the third to be
appointed by the two appointed arbitrators.

The third member of the Tribunal shall be appointed as soon as practicable (and
no later than 28 days) after the appointment of the two party-appointed
arbitrators. The Tribunal shall be constituted upon the appointment of the third
arbitrator.

The Arbitrators shall be persons (including those who have retired) with not
less than ten years' experience of insurance or reinsurance within the industry
or as lawyers or other professional advisers serving the industry.

Where a Party fails to appoint an arbitrator within 14 days of being called upon
to do so or where the two party-appointed arbitrators fail to appoint a third
within 28 days of their appointment, then upon application ARIAS (UK) will
appoint an arbitrator to fill the vacancy. At any time prior to appointment by
ARIAS (UK) the Party or arbitrators in default may make such appointment.

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The Tribunal may in its sole discretion make such orders and directions as it
considers to be necessary for the final determination of the matters in dispute.
The Tribunal shall have the widest discretion permitted under the law governing
the arbitral procedure when making such order or directions.

The seat of arbitration shall be London.

ARTICLE 11 -INSOLVENCY

Where an Insolvency Event occurs in relation to the Retrocedant the following
terms shall apply (and, in the event of any inconsistency between these terms
and any other terms of this Agreement, these terms shall prevail):

(1)   Notwithstanding any requirement in this Agreement that the Retrocedant
      shall actually make payment in discharge of its liability to its
      policyholder before becoming entitled to payment form the
      Retrocessionaire:

      (a)   the Retrocessionaire shall be liable to pay the Retrocedant even
            though the Retrocedant is unable actually to pay, or discharge its
            liability to its policyholder, but;

      (b)   nothing in this clause shall operate to accelerate the date for
            payment by the Retrocessionaire of any sum which may be payable to
            the Retrocedant, which sum shall only become payable as and when the
            Retrocedant would have discharged, by actual payment, its liability
            for its current net loss but for it being the subject of any
            Insolvency Event.

(2)   The existence, quantum, valuation and date for payment of any sum which
      the Retrocessionaire are liable to pay the Retrocedant under this
      Agreement shall be those and only those for which the Retrocessionaire
      would be liable to the Retrocedant if the liability of the Retrocedant to
      its policyholder had been determined without reference to any term in any
      composition or scheme of arrangement or any similar such arrangement,
      entered into between the Retrocedant and all or any part of its
      policyholder unless and until the Retrocessionaire serve written notice to
      the contrary on the Retrocedant in relation to any composition or scheme
      of arrangement.

(3)   The Retrocessionaire shall be entitled (but not obliged) to set-off,
      against any sum which it may be liable to pay the Retrocedant, any sum for
      which the Retrocedant is liable to pay the Retrocessionaire.

An Insolvency Event shall occur if:

(A)   (i)   (in relation to (1), (2) and (3) above) a winding up petition is
            presented in respect of the Retrocedant or a provisional liquidation
            is appointed over it or if the Retrocedant goes into administration,
            administrative receivership or receivership or if the Retrocedant
            has a scheme of arrangement or voluntary arrangement proposed in
            relation to all or any part of its affairs; or

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      (ii)  (in relation to (1) above) if the Retrocedant goes into compulsory
            or voluntary liquidation;

or, in each case, if the Retrocedant becomes subject to any other similar
insolvency process (whether under the laws of England and Wales or elsewhere)
and the Retrocedant is unable to pay its debts as and when they fall due within
the meaning of section 123 of the Insolvency Act 1986 (or any statutory
amendment or re-enactment of that section).

ARTICLE 12 -OFFSET

The Retrocedant and the Retrocessionaire shall have the right to offset any
balance or amounts due from one party to the other under the terms of this
Agreement. The party asserting the right of offset may exercise such right at
any time whether the balances due are on account of premiums, losses or
otherwise.

ARTICLE 13 - ERRORS AND OMISSIONS

Any inadvertent delay, omission, error or failure made in connection with this
Agreement shall not relieve either party hereto from any liability which would
attach hereunder if such delay, omission, error or failure had not been made.

ARTICLE 14 - SECURITY

As a condition precedent to this Agreement, Retrocessionaire shall execute:

      A.    the custody and investment accounting agreement with State Street
            Bank and Trust Company ("Custodian") in the form attached as
            Schedule 1 (the "Custody Agreement");

      B.    the control agreement between Retrocedent, Retrocessionaire and
            Custodian in the form attached as Schedule 2 (the "Control
            Agreement");

      C.    the discretionary investment advisory agreement with Alliance
            Capital Management L.P. ("Investment Manager") in the form attached
            as Schedule 3 (the "Investment Advisory Agreement"); and

      D.    the security agreement, pursuant to which Retrocessionaire grants a
            continuing first priority security interest in collateral accounts
            established with Custodian pursuant to the Custody Agreement, in the
            form attached as Schedule 4 (the "Security Agreement").

Retrocessionaire undertakes to notify Retrocedent in writing immediately upon
becoming aware of the occurrence of a Relevant Event under the Security
Agreement. Upon becoming aware of any such Relevant Event, Retrocedent shall be
entitled, upon notice in writing to Retrocessionaire, to terminate this
Agreement with immediate effect. Upon termination, Retrocessionaire shall within
seven days account to Retrocedent for all amounts owing to Retrocedent pursuant
to this Agreement, and the provisions of Article 12 (Offset) shall apply.

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No delay by Platinum UK in enforcing its rights under this Agreement or other
forbearance by Platinum UK shall be taken to be a waiver of such rights.

ARTICLE 15 - MISCELLANEOUS PROVISIONS

      A.    Severability. If any term or provision of this Agreement shall be
            held void, illegal, or unenforceable, the validity of the remaining
            portions or provisions shall not be affected thereby.

      B.    Successors and Assigns. This Agreement may not be assigned by either
            party without the prior written consent of the other. The provisions
            of this Agreement shall be binding upon and inure to the benefit of
            and be enforceable by the parties hereto and their respective
            successors and assigns as permitted herein.

      C.    Execution in Counterparts. This Agreement may be executed by the
            parties hereto in any number of counterparts and by each of the
            parties hereto in separate counterparts, each of which counterparts,
            when so executed and delivered, shall be deemed to be an original,
            but all such counterparts shall together constitute but one and the
            same instrument.

      D.    Headings. Headings used herein are not a part of this Agreement and
            shall not affect the terms hereof.

      E.    Amendments; Entire Agreement. This Agreement may be amended only by
            written agreement of the parties. This Agreement together with the
            Custody Agreement, the Control Agreement, the Investment Advisory
            Agreement and the Security Agreement supersede all prior discussions
            and written and oral agreements and constitutes the sole and entire
            agreement between the parties with respect to the subject matter
            hereof.

      F.    Governing Law. This Agreement shall be governed by the laws of
            England.

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ARTICLE 16 -

This contract replaces the earlier one signed on November 22, 2002

IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be executed
by their duly authorized representatives as of the date first above written.

                                        Platinum Underwriters Bermuda, Ltd.

                                        By: /s/ Francois Bertrand
                                            -----------------------------------
                                            Name: Francois Bertrand
                                            Title: Senior Vice President

                                        Platinum Re (UK) Limited

                                        By: /s/ Tom Mahoney
                                            ------------------------------------
                                            Name: Tom Mahoney
                                            Title: Managing Director

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                     Addendum A to the Quota Share Agreement
              by and between Platinum Underwriters Bermuda Limited
                          and Platinum Re (UK) Limited

25% Quota Share of Business Classified by the Retrocedant as International
Property Catastrophe Excess of Loss Business covering the Retrocedant's
participation in programmes providing coverage for losses occurring in the
United Kingdom and Eire.

                                       8<PAGE>

                                                                   EXHIBIT 10.19

                                 ADDENDUM NO. 1

                                     TO THE

                        QUOTA SHARE REINSURANCE AGREEMENT
                           DATED AS OF MARCH 27, 2003

              (HEREINAFTER REFERRED TO AS THE "ORIGINAL AGREEMENT")

                                     BETWEEN

                            PLATINUM RE (UK) LIMITED

                   (HEREINAFTER REFERRED TO AS THE "COMPANY")

                                       AND

                       PLATINUM UNDERWRITERS BERMUDA, LTD

                  (HEREINAFTER REFERRED TO AS THE "REINSURER")

WHEREAS, the Reinsurer and the Company are parties to the Original Agreement.

NOW THEREFORE, effective April 1, 2003, the parties hereto hereby agree to amend
the Original Agreement as follows:

      Addendum A - The first and only paragraph shall be deleted in its entirety
      and replaced with the following:

      "1.   25% Quota Share of Business classified by the Retrocedant as
            International Property Catastrophe Excess of Loss Business arising
            out of the Retrocedants participation in programmes from Cedant's
            domiciled in the United Kingdom and Eire.

      2.    Property Catastrophe Excess of loss treaty $40,000,000 excess of
            $50,000,000 any one occurrence between the Company and Platinum
            Underwriters Re, Inc."

All other terms and conditions of the Original Agreement remain unchanged.

                                                                     Page 1 of 2

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In Witness Whereof, the parties hereto have caused this Addendum No.1 to be
executed by their duly authorized representatives.

                                            Platinum Underwriters Bermuda, Ltd.

                                            By: /s/ Francois Bertrand
                                                -----------------------------
                                            Name: Francois Bertrand
                                            Title: Senior Vice President

                                            Platinum Re (UK) Limited

                                            By: /s/ Robert S. Porter
                                                -----------------------------
                                            Name: Robert S. Porter
                                            Title: Managing Director

                                                                     Page 2 of 2

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