Exhibit No. 10(a)

The Progressive Corporation
Executive Deferred Compensation Plan
Deferral Agreement

THIS DEFERRAL AGREEMENT is entered into pursuant to the provisions of The
Progressive Corporation Executive Deferred Compensation Plan (“Plan”). All
capitalized terms in this Agreement shall have the meanings ascribed to them in
the Plan.

1. Deferral Election. I hereby elect to defer receipt of the following portion
of my Gainsharing Award (Eligible Incentive Plans include: The Progressive
Corporation 2005 Gainsharing Plan; The Progressive Corporation 2005 Information
Technology Incentive Plan; The 2005 Progressive Capital Management Bonus Plan;
and The Progressive Corporation 2004 Executive Bonus Plan) earned in respect to
the year ending December 31, 2005 (select one and enter any desired percentage
not less than 10%)

     I elect to defer                     % of my entire Gainsharing Award OR

     I elect to defer                     % of that portion, if any, of my
Gainsharing Award that exceeds $                    .

2. Fixed Deferral Period. (The Plan gives you the option of electing a Fixed
Deferral Period. If you elect a Fixed Deferral Period, the balance of your
Deferral Account established pursuant to this Agreement will be distributed to
you within 30 days after the end of the Fixed Deferral Period, or, if earlier,
the date you die or incur a Termination of Employment or the date a Change in
Control occurs. If you do not elect a Fixed Deferral Period, your Account will
be distributed upon the earlier of the date you die or incur a Termination of
Employment or the date a Change in Control occurs.) However, for certain
executives, distributions due to Termination of Employment will not be made
until six months after the employment termination date.

Please select one of the following:

I elect a Fixed Deferral Period ending on                     (Must be a date at
least 3 years after the end of the calendar year in which the Gainsharing Award
is earned — January 1, 2009 or later)

OR

                                   I do not wish to elect a Fixed Deferral
Period.

3. Method of Distribution. I hereby elect that any distribution of the balance
of the Deferral Account established pursuant to this Agreement made on account
of Termination of Employment or expiration of a Fixed Deferral Period be paid as
follows: (check one)

                                   in a single lump sum payment

OR in

               Three annual installments                    

               Five annual installments                    

               Ten annual installments                    

I understand that Plan distributions made on account of reasons other than
Termination of Employment or expiration of a Fixed Deferral Period will be made
in a single lump sum payment, unless the Plan provides otherwise. I understand
that I may change the method of distribution elected above only if and to the
extent permitted by the Plan.

 

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     4. Investment Election. I direct that the amount I have deferred pursuant
to Section 1 of this Agreement shall be deemed to be invested in the following
Investment Funds in the percentages indicated: (must be increments of 1%)

     
                   %
  Fidelity Retirement Money Market Portfolio
                   %
  PIMCO Total Return Fund — Administrative Class (1)
                   %
  Oakmark Equity and Income Fund — Class 1
                   %
  Washington Mutual Investors Fund — Class A
                   %
  Fidelity Dividend Growth Fund
                   %
  Vanguard Institutional Index Fund — Institutional Class
                   %
  Fidelity Mid-Cap Stock Fund (2)
                   %
  American AAdvantage Small Cap Value Fund — Plan Ahead Class
                   %
  FMA Small Company Portfolio-Institutional Class
                   %
  Wasatch Small Cap Growth Fund
                   %
  Fidelity Diversified International Fund (3)
                   %
  Templeton World Fund — Class A (4)
                   %
  The Progressive Corporation Stock Fund
100%
  TOTAL

(1) There is a short-term trading fee of 2.0% for shares held less than 7 days
on the PIMCO Total Return Fund — Administrative Class.

(2) There is a short-term trading fee of 0.75% for shares held less than 30 days
on Fidelity Mid-Cap Stock Fund.

(3) There is a short-term trading fee of 1.0% for shares held less than 30 days
on Fidelity Diversified International Fund.

(4) There is a short-term trading fee of 2.0% for shares held less than 7 days
on the Templeton World Fund — Class A.

I understand that I may transfer amounts among Investment Funds only to the
extent permitted by the Plan. I also understand that this investment election is
merely a device used to determine the amount payable to me under the Plan and
does not provide me with any actual rights or interests in any particular funds,
securities or property of the Company, any Affiliated Company or the Trust, in
any stock of The Progressive Corporation or in any investment funds offered
under the Plan. I also understand that my right to receive distributions under
the Plan makes me a general creditor of the Company with no greater priority
than any other general creditor of the Company.

5. Miscellaneous. I understand that this Agreement is subject to the terms,
conditions and limitations of the Plan, as in effect from time to time, in all
respects and that, except as expressly permitted by the Plan, all elections made
in this Agreement are irrevocable. I acknowledge that I have received, read and
understand the Plan Description dated December, 2004 relating to the Plan. I
agree to accept as final and binding all decisions and interpretations of the
Committee relating to the Plan, the Trust and this Agreement.

ALSO, I UNDERSTAND THAT THE PLAN IS LIKELY TO BE AMENDED IN SIGNIFICANT RESPECTS
FOLLOWING MY EXECUTION OF THIS AGREEMENT. I AGREE TO BE BOUND BY ALL SUCH
AMENDMENTS AND BY ANY CHANGES SUCH AMENDMENTS MAY REQUIRE IN THE TERMS AND
CONDITIONS OF THIS AGREEMENT.

NAME OF ELIGIBLE EXECUTIVE:
DATE:
SSN:

Your electronic submission of this Election Form will create a date/time stamp
and serve as your signature