<PAGE>
                                                                    Exhibit 10.2

January 9, 2001

Mr. Frank Patchel
11 Dorothy Place
Berkeley, CA 94705

Re:  Terms of Employment Offer with Mediaplex, Inc.

Dear Frank:

  Mediaplex, Inc, (the "Company"), is pleased to offer you the position
described below.  This letter sets forth the terms and conditions of your
employment with the Company and is subject to the satisfactory completion of
background and reference checks currently underway.

  I.  Description of Employment Position and Responsibilities.  You will serve
in the position of Chief Financial Officer.  By executing this agreement, you
agree to assume and discharge such duties and responsibilities as are
commensurate with this position and such other duties and responsibilities that
are assigned to you from time to time by the Company's Board of Directors, Chief
Executive Officer, or your then supervisor.  During the term of your employment,
you shall devote your full time, skill and attention to your duties and
responsibilities and shall perform them faithfully, diligently and competently.
In addition, you shall comply with and be bound by the operating policies,
procedures and practices of the Company in effect from time to time during your
employment.

  II.  Employment Considerations.

  2.1  At-Will Employment.  You acknowledge that your employment with the
Company is for an unspecified duration that constitutes at-will employment, and
that either you or the Company can terminate this relationship at any time, with
or without cause and without notice.

  2.2  Employment Eligibility. Your employment is contingent on your submission
to the Company of satisfactory original documentation to verify your identity
and eligibility for employment in the United States.

  III.  Compensation.

  3.1  Base Salary.  In consideration of your services, effective January 15,
2001, you will be paid an annual base salary of $200,000 (Two Hundred Thousand
Dollars and no Cents), payable no less frequently than on a monthly basis in
accordance with the Company's standard payroll practices.  Your base salary, in
conjunction with your performance evaluation, is normally reviewed annually by
appropriate managers of the Company.

  3.2  Incentive Compensation.  In addition to your base salary, you may be
entitled to participate in such incentive compensation plan that may be adopted
by the Company in its sole discretion.  You understand that the adoption of any
such plan, the eligibility and measurement criteria and all other terms shall be
at the sole discretion of the Company. You will be eligible to receive a bonus
of up to 25% (Twenty-Five Percent) of your Base Salary upon the achievement of
certain milestones to be established by your supervisor within thirty (30) days
of your date of commencement with the Company.

      For the fiscal year ending 31 December 2001, your bonus will be payable
upon completion to the satisfaction of the CEO, of the following objectives, and
according to the indicated proportion of the total bonus:

  20%  Equity Line of Credit in Q1
  20%  Evaluation of and Conversion to AdWare FinPro 6 for Mediaplex in Q1
  10%  Maintenance of Company Adherence to Budget for 2001 and timely variance
       reporting
  10%  Successful Purchase Order Management of Consultants & Contractors
  10%  Evaluation and negotiation of timely sublets for the NY/San Jose offices
  10%  Timely bill/pay recon
  10%  Implementation of a weekly sales-to-date and sales forecasting system
<PAGE>

  10%  Timely SEC filings, management reports (by 15th of following month),
production of flash financial results (Sales and Operating Profit) (by 3rd of
following month).

  3.3  Termination.  If your employment is terminated by the Company for any
reason, with or without cause, or if you resign your employment voluntarily, no
compensation or other payments will be paid or provided to you for periods
following the date when such a termination of employment is effective, provided
that any rights you may have under the benefit plans of the Company shall be
determined under the provisions of those plans.  If your employment terminates
as a result of your death or disability, no compensation or payments will be
made to you other than those to which you may otherwise be entitled under the
benefit plans of the Company.

  IV.  Additional Benefits.

  4.1  Health Insurance/Vacation/Benefit Plans. You will be entitled to receive
the standard employee benefits made available by the Company to its employees to
the full extent of your eligibility therefor.  You shall be entitled to three
(3) weeks of paid personal time off ("PTO") per year, which may be accumulated
to a maximum of 180 hours; the terms and conditions of your benefits shall be in
accordance with the Company's PTO policy in effect at that time.  During your
employment, you shall be permitted, to the extent eligible, to participate in
any group medical, dental, life insurance and disability insurance plans, or
similar benefit plan of the Company that is available to employees generally.
Participation in any such plan shall be consistent with your rate of
compensation to the extent that compensation is a determinative factor with
respect to coverage under any such plan.

  4.2  Reimbursed Expenses.  The Company shall reimburse you for all reasonable
expenses actually incurred or paid by you in the performance of your services on
behalf of the Company, upon prior authorization and approval in accordance with
the Company's expense reimbursement policy as from time to time in effect.

  4.3  Stock Options.  Pursuant to Board approval, and under the terms and
conditions of the Company's Stock Option Plan and Stock Option Agreement,
including the stock vesting provisions contained therein, you will be granted an
option to purchase 100,000 shares of common stock of the Company.  You will be
granted an option to purchase an additional 50,000 shares of common stock of the
Company for the fiscal year ending 31 December 2001, upon completion to the
satisfaction of the CEO, of the objectives and according to the indicated
proportion of the total options as outlined for your bonus in Section 3.2
herein.  The Company Stock Option Plan, including the Stock Option Agreement,
will be sent to you separately.

  V.  Termination; Change of Control Benefits.

  5.1  Voluntary Termination; Cause.  At any time, if your employment is
terminated by the Company with Cause, or if you resign your employment
voluntarily, no compensation or other payments will be paid or provided to you
for periods following the date when such a termination of employment is
effective, provided that any rights you may have under the benefit plans of the
Company shall be determined under the provisions of those plans.  If your
employment terminates as a result of your death or disability, no compensation
or payments will be made to you other than those to which you may otherwise be
entitled under the benefit plans of the Company.

  5.2  Change of Control Compensation.  In the event there should occur a Change
of Control (as defined below), and (i) your employment by the Company terminates
for any reason other than for Cause or on account of your permanent disability
or death or (ii) there occurs a Constructive Termination the Company will pay to
you as severance, in one lump sum amount (unless you indicate in writing to the
Company prior to the Company's payment of your election to be paid in
installments over a specified period) an amount equal to five (5) months of your
annual base salary in effect immediately prior to the time of such termination.
Such amount will be paid by the Company as soon as administratively possible
following such termination, but in all events not later than fifteen (15) days
following the effective date of such termination.  Such amounts paid will be
reduced by all applicable withholding taxes and other deductions required by law
and any additional amounts authorized by you to be withheld.

  5.3  Other Change of Control Benefits.  In addition to any amounts payable
under Section 5.2 above, for a period of four (4) months following termination
of employment, the Company will continue to provide you with, and pay the same
portion of the cost as is then paid by the Company as of the termination date of
health, disability and life insurance coverage for you, your spouse and
dependents that is commensurate with the coverage then
<PAGE>

provided to you at the time of termination. The Company will structure such
health, disability and life insurance coverage as nontaxable benefits to the
maximum extent possible, including, but not limited to, by characterizing such
benefits as coverage to a former employee. Specifically for health insurance
coverage to the extent permitted by the Consolidated Omnibus Budget
Reconciliation Act of 1985 ("COBRA") and by the Company's group health insurance
policies, you will elect COBRA continuation coverage and the Company will pay
you and your covered dependents' COBRA continuation premiums for following the
date of termination of employment. You agree to notify the Vice President of
Human Resources of the Company in writing immediately upon the commencement of
health benefit coverage, which would cause your COBRA continuation coverage to
cease. This Section 5.3 provides only for the Company's payment of COBRA
continuation premiums for the periods specified above. This Section V is not
intended to affect, nor does it affect, the rights of you, or your covered
dependents under any applicable law with respect to health insurance
continuation coverage.

  5.4  Outplacement Services.  In addition, the Company will, at its sole
expense as incurred, for a period of four (4) months following termination of
employment, provide you with outplacement services the scope and provider of
which will be selected by you in your sole discretion.

  5.5  Change in Control Definitions.  For purposes of this Agreement:

  (a) A "Change in Control" will be deemed to occur upon consummation of any one
of the following:

     (i) a sale, lease or other disposition of all or substantially all of the
  assets of the Company;

     (ii) a merger, consolidation or other reorganization in which the Company
  is not the surviving corporation and the stockholders of the Company
  immediately prior to the merger, consolidation or other reorganization fail to
  possess direct or indirect ownership of more than fifty percent (50%) of the
  voting power of the securities of the surviving corporation (or if the
  surviving corporation is a controlled affiliate of another Person, then the
  required beneficial ownership will be determined with respect to the
  securities of that Person which controls the surviving corporation and is not
  itself a controlled affiliate of any other Person) immediately following such
  transaction;

     (iii)  a merger, consolidation or other reorganization in which the Company
  is the surviving corporation and the stockholders of the Company immediately
  prior to such merger, consolidation or other reorganization fail to possess
  direct or indirect beneficial ownership of more than fifty percent (50%) of
  the securities of the Company (or if the Company is a controlled affiliate of
  another Person, then the required beneficial ownership will be determined with
  respect to the securities of that Person which controls the Company and is not
  itself a controlled affiliate of any other Person) immediately following such
  transaction;

     (iv) any transaction or series of related transactions after which any
  person (as such term is defined in Section 13(d)(3) of the Securities Exchange
  Act of 1934, as amended (the "Exchange Act")), other than any employee benefit
  plan or related trust sponsored or maintained by the Company or any subsidiary
  of the Company, becomes the beneficial owner (within the meaning of Rule 13d-3
  under the Exchange Act or comparable successor rule) of voting securities of
  the Company representing thirty percent (30%) or more of the combined voting
  power of all of the voting securities of the Company;

     (v) the individuals who, as of the date immediately following the Company's
  2000 Annual Meeting of Stockholders, are members of the Company's Board of
  Directors (the "Incumbent Board") cease for any reason to constitute at least
  fifty percent (50%) thereof. (If the election, or nomination for election by
  the Company's stockholders, of any new director was approved by a vote of at
  least two-thirds (2/3) of the Incumbent Board, such new director will be
  considered as a member of the Incumbent Board); and

     (vi) the liquidation or dissolution of the Company.

  For purposes of Sections 5.5(a)(ii) and 5.5(a)(iii) above, any Person who
acquired securities of the Company prior to the occurrence of the specified
transaction in contemplation of such transaction and who immediately after such
transaction possesses direct or indirect beneficial ownership of at least ten
percent (10%) of the securities of the Company or the surviving corporation, as
appropriate (or if the Company or the surviving corporation is a controlled
<PAGE>

affiliate, then of the appropriate Person as determined above), will not be
included in the group of stockholders of the Company immediately prior to such
transaction.

  (b) A "Constructive Termination" means any of the following occurring after a
Change in Control:

     (i) a reduction, without your written consent, in your then current annual
  base salary;

     (ii) a relocation of your principal place of employment by more than
  twenty-five (25) miles, unless you consent in writing to such relocation; and

     (iii)  any material breach by the Company of any provision of this offer
  letter after written notice delivered to the Company of such breach and a
  reasonable opportunity to cure such breach (which opportunity shall not extend
  beyond a period of thirty (30) days from the date of delivery of such written
  notice).

  (c) "Cause" means (i) a conviction of a felony or a crime involving moral
turpitude causing material harm to the standing and reputation of the Company or
(ii) any willful misconduct in the performance of your duties to the Company
where such willful misconduct has resulted in substantial and material damage to
the Company or its successor or the Person whose transactions caused the Change
in Control or any of their respective subsidiaries, as determined by the Board
of Directors of the Company and as stated in a written notice from the Company
to you.

  (d) "Person" means an individual, corporation, partnership, limited liability
company, association, trust, unincorporated organization or other legal entity
including any governmental entity.

  VI.  Continuation of Employment and Cooperation with the Company after Change
in Control.   Following a Change in Control, you agree that you will continue to
provide your services as an employee of the Company (or the successor to the
Company), as requested, as previously provided prior to the Change in Control or
such performance as is reasonably requested by the Company (or its successor)
and is substantially similar as your duties prior to such Change in Control; and
to cooperate with the Company (or its successor) in all matters relating to any
winding up of your pending work on behalf of the Company (or its successor) and
the orderly transfer of any such pending work to other employees of the Company
(or its successor) as may be designated by the Company (or its successor), which
period will not exceed ninety (90) days.  Furthermore, you agree to return all
property of the Company in your possession or control to the Company (or its
successor) as promptly as practicable within ten (10) days after the effective
date of your termination of employment, except to the extent that retention of
any of such property is necessary or desirable or convenient in order to permit
you to satisfy your obligations under this Section VI.  The performance your
obligations under this Section VI shall be a condition to any and all of the
benefits payable or otherwise granted to you upon a termination of your
employment after a Change in Control pursuant to Section VI hereof.]

  VII.  Intellectual Property Rights/Confidential Information.

  5.1  Valuable Trade Secrets.  You agree that the Company is the owner of
valuable trade secrets, client, vendor, customer and contractor lists and other
confidential and proprietary information.  As such, you agree that your
employment is contingent upon your execution of, and delivery to, the Company of
a Confidential Information and Invention Assignment Agreement ("Intellectual
Property Agreement") in the standard form utilized by the Company.

  5.2  Additional Confidential Information.  You agree to maintain the
confidentiality ofall elements of this Agreement, agreeing to an absolute
prohibition on any disclosure or use of such information in any fashion, with
the exception of discussions with your supervisor or myself, or the Company's
Human Resources Department or Legal Department.  As you are well aware the
maintenance of confidentiality of this kind of information is critical to our
organization.

  5.3  Equitable Remedies.  You agree that it would be impossible or inadequate
to measure and calculate the Company's damages from any breach of the covenants
set forth in this Section as well as Sections 1, 2, 3, and 5 of the Intellectual
Property Agreement.  Accordingly, you agree that if you breach any of such
Sections, the Company will have available, in addition to any other right or
remedy available, the right to obtain an injunction from a court
<PAGE>

of competent jurisdiction restraining such breach or threatened breach and to
specific performance of any such provision of this Agreement. You further agree
that no bond or other security shall be required in obtaining, such equitable
relief and you hereby consent to the issuance of such injunction and to the
ordering of specific performance.

  VIII.  Non-Competition/Conflicting Employment.  You agree that, during the
term of your employment with the Company, you will not engage in any other
employment, occupation, consulting or other business activity directly related
to the business in which the Company and/or its customers are now involved or
become involved during the term of your employment, nor will you engage in any
other activities that conflict with your obligations to the Company.

  IX.  Arbitration.  Except as otherwise provided in Section 5.3 above, it is
agreed that any dispute or controversy arising out of or relating to any
interpretation, construction, performance or breach of this Agreement, shall be
exclusively settled by confidential arbitration to be held in San Francisco
County, California, in accordance with the rules then in effect of the American
Arbitration Association.  The arbitrator may grant injunctions or other relief
in such dispute or controversy.  The decision of the arbitrator shall be final,
conclusive and binding on the parties to the arbitration.  Judgement may be
entered on the arbitrator's decision in any court having jurisdiction.  Each
party shall pay one-half of the costs and expenses of such arbitration, and each
of us shall separately pay our counsel fees and expenses.

  X.  General Provisions.

  8.1  Governing Law.  This offer letter will be governed by the laws of the
State of California.

  8.2  Entire Agreement.  This offer letter sets forth the entire agreement and
understanding between the Company and you relating to your employment and
supersedes all prior verbal discussion and written agreements between us.  Any
subsequent change or changes in your duties, salary or other compensation will
not affect the validity or scope of this agreement.  Any change to the at-will
term of this agreement must be executed in writing and signed by you and the
Chief Executive Officer or President of the Company.

  8.3  Successors/Assigns.  This agreement will be binding upon your heirs,
executors, administrators and other legal representatives and will be for the
benefit of the Company and its respective successors and assigns.

  Please acknowledge and confirm your acceptance of this letter by signing and
returning the enclosed copy of this offer letter, and the Confidential
Information and Invention Assignment Agreement as soon as possible. This offer
shall expire at 5:00 p.m. on January 11, 2001 if not accepted by you and
executed and returned below prior to that time.

  If you have any questions about this offer letter, please call me directly.

  MEDIAPLEX, INC.

                                 By: /s/ Gregory R. Raifman
                                     -----------------------------
                                     Gregory R. Raifman
                                     CEO and Chairman of the Board

  ACCEPTANCE:

  I accept the terms of my employment with Mediaplex, Inc. as set forth herein.
I understand that this offer letter does not constitute a contract of employment
for any specified period of time, and that my employment relationship may be
terminated by either party, with or without cause and with or without notice.

  ACCEPTED AND AGREED:

  /s/ Frank Patchel             Date:    1/9/01
  --------------------                  --------
  Frank Patchel