<PAGE>

                                                                   EXHIBIT 10.4a

                    SECOND AMENDMENT TO EMPLOYMENT AGREEMENT
                    ----------------------------------------

     THAT EMPLOYMENT AGREEMENT ("Agreement") made as of the 1st day of August,
1994, by and between THE WISER OIL COMPANY OF CANADA, a Canadian corporation,
and ALLEN J. SIMUS is hereby amended in the following respects only:

     FIRST:  Section 1.02 of the Agreement is hereby amended by restatement in
     -----
its entirety to read as follows:

     1.02.    Term.  Subject to the terms and provisions of Article II hereof,
              ----
     Employee's employment hereunder shall be extended and shall continue
     through the close of business on March 31, 2000.

     SECOND:  Article I of the Agreement is hereby amended to add a new Section
     ------
1.05 to the end thereof to read as follows:

     1.05.    Certain Additional Payments by the Company.  Anything in this
              ------------------------------------------
     Agreement to the contrary notwithstanding, if it shall be determined that
     any payment or distribution by the Company to or for the benefit of
     Employee (whether paid or payable or distributed or distributable pursuant
     to the terms of this Agreement or otherwise) but determined without regard
     to any additional payments required pursuant to this Section 1.05 (a
     "Payment") would be subject to the excise tax imposed by Section 4999 of
     the Internal Revenue Code of 1986, as amended (the "Code"), or any interest
     or penalties are incurred by Employee with respect to such excise tax (such
     excise tax, together with any such interest and penalties, hereinafter
     collectively referred to as the "Excise Tax"), then Employee shall be
     entitled to receive an additional payment from the Company (a "Gross-Up
     Payment") in an amount such that after payment by Employee of all taxes
     (including any interest or penalties with respect to such taxes),
     including, without limitation, any income taxes (and any interest and
     penalties imposed with respect thereto) and Excise Tax imposed upon the
     Gross-Up Payment, Employee retains an amount of Gross-Up Payment equal to
     the Excise Tax imposed upon the Payments.

     THIRD:  Section 2.05 of the Agreement is hereby amended by redesignating as
     -----
subsection (b) the second subsection appearing therein designated as subsection
(a), redesignating as subsection (c) the subsection therein designated as
subsection (b), and restating subsection (a) thereof in its entirety to read as
follows:
          (a) If Employee's employment with the Company is terminated by the
     Company or by Employee for any reason other than illness, disability or
     death of
<PAGE>

     Employee within twelve months following a Change of Control of the Company
     or the Parent Company, Employee shall be paid, within 30 days following
     such termination, an amount in cash equal to the sum of (i) Employee's Base
     Salary at the time of his termination of employment multiplied by three,
     (ii) the amount equal to the premium cost or other amount paid by the
     Company during the one-year period preceding Employee's termination of
     employment to provide Employee with (A) life, health and disability
     insurance benefits, and (B) the use of an automobile for such year, and
     (iii) the amount of the additional payment, if any, determined pursuant to
     Section 1.05.

     IN WITNESS WHEREOF, this Amendment has been executed this 20th day of May,
1997, to be effective as of April 1, 1997.





                              -------------------------------------
                              ALLEN J. SIMUS


                              THE WISER OIL COMPANY OF CANADA



                              By
                                 ----------------------------------
                                 Title:

                                       2