<PAGE>   1
                                                                   EXHIBIT 10.15


                         EXECUTIVE EMPLOYMENT AGREEMENT

         This Executive Employment Agreement (the "Agreement") is made the 29th
day of January, 1998, by and between National Energy Group, Inc., a Delaware
corporation acting by and through its hereunto duly authorized officer (the
"Company"), and Frederic R. Miller (the "Executive").

         WHEREAS, the Executive is presently in the employ of the Company in the
capacity of Senior Vice President of Finance and Administration and Chief
Financial Officer, and the Company is willing to provide certain employment
assurances to the Executive in the event of a Change of Control (as defined
below) of the Company as incentive and inducement for the Executive to continue
in such employment in his present capacity after a Change of Control; and

         WHEREAS, in consideration of such employment assurances, the Executive
is willing to remain in the employ of the Company in the capacity of Senior Vice
President of Finance and Administration and Chief Financial Officer after a
Change of Control of the Company.

         NOW, THEREFORE, in consideration of the premises and the mutual terms
and conditions hereof, the Company and the Executive hereby agree as follows:

         1. Employment. In consideration of the benefits hereinafter specified,
the Executive hereby agrees to continue his employment with the Company in the
capacity of Senior Vice President of Finance and Administration and Chief
Financial Officer after a Change of Control of the Company and to discharge his
duties in such capacity during the term of this Agreement.

         2. Exclusive Services. The Executive shall devote his full working
time, ability and attention to the business of the Company during the term of
this Agreement and shall not, directly or indirectly, render any services of a
business, commercial or professional nature to any other person, corporation or
organization, whether for compensation or otherwise, without the prior knowledge
and consent of the Board of Directors (the "Board") or President and Chief
Executive Officer of the Company; provided, however, that the provisions of this
Agreement shall not be construed as preventing the Executive from investing in
other non-competitive businesses or enterprises if such investments do not
require substantial services on the part of the Executive in the affairs or
operations of any such business or enterprise so as to significantly diminish
the performance by the Executive of his duties, functions and responsibilities
under this Agreement. During the term of this Agreement, the Executive shall
not, directly or indirectly, either through any kind of ownership (other than
ownership of securities of publicly held corporations of which the Executive
owns less than five percent (5%) of any class of outstanding securities) or as a
director, officer, agent, employee or consultant engage in any business that is
competitive with the Company.

         3. Authority and Duties. During the term of this Agreement, the
Executive shall have such authority and shall perform such duties, functions and
responsibilities as are specified by the Bylaws of the Company, the Executive
Committee, the Board of Directors, or the President of the Company and/or as are
appropriate for the office of the Senior Vice President of Finance and
Administration and Chief Financial Officer and shall serve with the necessary
power and authority commensurate with such position. If the Company removes the
Executive from the office of the Senior Vice President of Finance and
Administration and Chief Financial Officer of the Company after a Change of
Control or limits, restricts or reassigns his authority and responsibility after
a Change of Control so as to be less significant than, or not comparable to,
that to which he held immediately preceding such Change of Control in his
capacity as Senior Vice President of Finance and Administration and Chief
Financial Officer without his prior mutual consent, the Executive 




<PAGE>   2

shall be entitled to resign for good reason and receive the Severance Benefits
set forth in this Agreement.

         4. Compensation. In consideration for the services to be rendered by
the Executive to the Company and/or its subsidiaries, the Company shall pay to
the Executive at least the gross cash compensation and shall award to the
Executive at least the bonuses as set forth below:

<TABLE>
<CAPTION>
==================================================================================================================================

             ANNUAL PERIOD                                 ANNUAL                                ANNUAL BONUS
                                                         BASE SALARY
----------------------------------------------------------------------------------------------------------------------------------

<S>                                       <C>                                         <C>                                  
For the one year period following         100% of the average of the Executive's      100% of the average of the bonuses   
effective date of a Change of Control     annual base salary in effect immediately    paid to the Executive for each of the
                                          prior to the Change in Control and of       three fiscal years before the Change 
                                          the Executive's annual base salary for      in Control                           
                                          each of the immediately preceding two                                            
                                          years                                       
                                          
----------------------------------------------------------------------------------------------------------------------------------

For the second year following effective   100% of the average of the Executive's      100% of the average of the bonuses paid
date of a Change of Control               annual base salary on the date that is      to the Executive for the three         
                                          one year after the Change in Control and    immediately preceding fiscal years     
                                          of the Executive's annual base salary       
                                          for each of the immediately preceding    
                                          two years                                
                                          
----------------------------------------------------------------------------------------------------------------------------------

For the third year following effective    100% of the average of the Executive's      100% of the average of the bonuses paid
date of a Change of Control               annual base salary on the date that is      to the Executive for the three         
                                          two years after the Change in Control and   immediately preceding fiscal years     
                                          of the Executive's annual base salary       
                                          for each of the immediately preceding two
                                          years                                    
                                          
==================================================================================================================================
</TABLE>


In the event that the Executive shall not have been employed for three years
prior to the effective date of this Agreement, the Executive's annual base
compensation rate or bonus rate shall be averaged over the actual period of
employment of the Executive by the Company.

         Each of the annual base salary amounts set forth above shall be paid to
the Executive in equal monthly installments, or as otherwise agreed, during each
corresponding year of the term of this Agreement, provided that for any period
of less than one (1) year, the annual base salary shall be pro-rated
accordingly. The annual bonus amount indicated above or amounts in excess of
such indicated bonus shall be awarded no later than December 31 of the
corresponding annual period. The amount set forth above is compensation to the
Executive or gross amounts due hereunder, and the Company shall have the right
to deduct therefrom all taxes and other amounts which may be required to be
deducted or withheld by law (including, but not limited to, income tax,
withholding, social security and medicare payments) whether such law is now in
effect or becomes effective after the execution of this Agreement.

         5. Benefits and Business Expenses. During the term hereof:

                  (a) The Executive shall be entitled to continue his
         participation in programs maintained by the Company for the benefit of
         its employees and officers and to participate in new or amended
         programs, including, but not limited to, medical, health, life,
         accident and disability insurance programs, pension plans, incentive
         compensation plans, stock 


                                       2
<PAGE>   3

         option plans, stock appreciation rights plans, and limited stock 
         appreciation rights plans. The Company shall not terminate nor amend 
         such plans to the detriment of the Executive.

                  (b) To the extent that the Company has provided the Officer
         with an automobile, club memberships, association and trade memberships
         and other memberships prior to the Change of Control, the Company shall
         continue to provide the Officer with such items, of a comparable
         nature, following a Change of Control. The Company shall pay the
         expenses of such automobile, memberships and subscriptions.

                  (c) The Executive shall be reimbursed for any business
         expenses reasonably incurred in carrying out his duties, functions and
         responsibilities upon presentation of expense reports to the Company.

         6. Term. This Agreement shall have a term of three (3) years commencing
on the effective date of a Change of Control and shall be automatically extended
on the 9th day of each and every calendar month during the term of this
Agreement for an additional calendar month so that at the beginning of each and
every month during the term of this Agreement there shall be a remaining term of
three (3) years (but in no event beyond the time the Executive reaches age 65)
unless and until the Company gives written notice to the Executive that the term
of this Agreement shall not be further so extended, in which case the Executive
shall be entitled to resign for good reason. The provisions of this Section 6
shall apply to each Change of Control irrespective of any Changes of Control
which may have occurred previously.

         7. Severance Benefits After Change Of Control. In addition to such
compensation and other benefits payable to or provided for the Executive as
authorized by the Board from time to time, Executive shall be entitled to
receive in lieu of the compensation described in paragraph 4 hereof, and the
Company shall pay or provide to the Executive the following severance benefits
(the "Severance Benefits") in the event that, during the term hereof, the
Company discharges the Executive without cause or the Executive resigns for good
reason after a Change of Control, to-wit:

                  (a) The Company shall pay to the Executive a lump sum cash
         payment (multiplied by the applicable factor described below) payable
         on such date of termination of employment equal to the Executive's
         "base compensation" then in effect, which shall, and is defined to,
         consist of the sum of (i) the Executive's annual base salary then in
         effect, (ii) the average of the amounts of the last three annual cash
         bonuses paid or granted to, or earned by, the Executive, and (iii) the
         average of the total amounts of the Company's contributions to its
         retirement plan allocable to the Executive on a fully vested basis for
         the last three fiscal years of the retirement plan. The amount of the
         "base compensation" payable to the Executive pursuant to this Section
         7(a) shall be multiplied by the number three (3) for the purposes of
         determining the lump sum cash severance payment due under this Section
         7(a).

                  (b) All stock options granted by the Company to the Executive,
         all contributions made by the Executive and by the Company for the
         account of the Executive to any pension, retirement or any other
         benefit plan, and all other benefits or bonuses, including but not
         limited to net profits interests which contain vesting or
         exercisability provisions conditioned upon or subject to the continued
         employment of the Executive, shall become fully vested and exercisable
         and shall remain fully exercisable for a period of the later of three
         hundred sixty (360) days after (i) the date of such termination of
         employment, or (ii) the termination of this Agreement.


                                       3
<PAGE>   4

                  (c) The Company shall continue the participation of the
         Executive in all life, accident, disability, medical, dental and all
         other health and casualty insurance plans maintained by the Company for
         its officers and employees for a period of one (1) year after the date
         of such termination of employment or for such longer period as may be
         required by applicable law.

                  (d) Notwithstanding any provision of this Agreement to the
         contrary, if the Executive is a disqualified individual (as the term
         "disqualified individual" is defined in Section 280G of the Code) and
         if any portion of the Severance Benefits under this Section 7 of this
         Agreement would be an excess parachute payment (as the term "excess
         parachute payment" is defined in Section 280G of the Code) but for the
         application of this sentence, then the amount of the Severance Benefits
         otherwise payable to the Executive pursuant to this Agreement will be
         reduced to the minimum extent necessary (but in no event to less than
         zero) so that no portion of the Severance Benefits, as so reduced,
         constitutes an excess parachute payment. The determination of whether
         any reduction in the amount of the Severance Benefits is required
         pursuant to this Section 7(d) will be made by the Company's independent
         accountants. The fact that the Executive has his Severance Benefits
         reduced as a result of the limitations set forth in this Section 7(d)
         will not of itself limit or otherwise affect any rights of the
         Executive arising other than pursuant to this Agreement.

                  (e) The Company has determined that the amounts payable under
         this Agreement constitute reasonable compensation for services
         rendered. Accordingly, notwithstanding any other provision hereof,
         unless such action would be expressly prohibited by applicable law, if
         any amount is paid pursuant to this Agreement which is determined to be
         subject to the excise tax imposed by Section 4999 of the Code, the
         Company will pay to the Executive an additional amount in cash equal to
         the amount necessary to cause the aggregate amount payable under this
         Agreement, including such additional cash payment (net of all federal,
         state and local income taxes and all taxes payable as the result of the
         application of Sections 280G and 4999 of the Code), to be equal to the
         aggregate amount payable under this Agreement, excluding such
         additional payment (net of all federal, state and local income taxes),
         as if Sections 280G and 4999 of the Code (and any successor provisions
         thereto) had not been enacted into law.

         8. Place of Performance. During the term hereof:

                  (a) The principal office of the Executive and the principal
         place for performance by him of his duties, functions and
         responsibilities under this Agreement shall be in the City or suburbs
         of Dallas, Texas.

                  (b) It is recognized that the performance of the Executive's
         duties hereunder may occasionally require the Executive, on behalf of
         the Company, to be away from his principal office for business reasons.
         Unless consent of the Executive is obtained, such periods of being away
         from his principal office on behalf of the Company shall not exceed
         thirty (30) calendar days per year.

         9. Definition of Change of Control. For purposes of this Agreement,
"Change of Control" shall mean the occurrence of one or more of the following
events: (i) a person or entity or group (as that term is used in Section
13(d)(3) of the Exchange Act) of persons or entities shall have become the
beneficial owner of a majority of the securities of the Company ordinarily
having 


                                       4
<PAGE>   5

the right to vote in the election of directors, (ii) during any consecutive
two-year period, individuals who at the beginning of such period constituted the
Board of Directors of the Company (together with any directors who are members
of such Board of Directors of the Company on the date hereof and any new
directors whose election by such Board of Directors of the Company or whose
nomination for election by the stockholders of the Company was approved by a
vote of 66b% of the directors then still in office who were either directors at
the beginning of such period or whose election or nomination for election was
previously so approved) cease for any reason to constitute a majority of the
Board of Directors of the Company then in office, (iii) any sale, lease,
exchange or other transfer (in one transaction or a series of related
transactions) of all, or substantially all, the assets of the Company to any
person or entity or group (as so defined in Section 13(d)(3) of the Exchange
Act) of persons or entities (other than any wholly owned subsidiary of the
Company), or (iv) the merger or consolidation of the Company into or with
another corporation or the merger of another corporation into the Company with
the effect that immediately after such transaction any person or entity or group
(as so defined in Section 13(d)(3) of the Exchange Act) of persons or entities,
or the stockholders of any other entity, shall have become the beneficial owner
of securities of the surviving corporation of such merger or consolidation
representing a majority of the voting power of the outstanding securities of the
surviving corporation ordinarily having the right to vote in the election of
directors. The Alexander Energy Corporation merger, however it might be
structured, shall not constitute a Change of Control under this Agreement.

         10. Discharge with Cause. For the purposes of this Agreement, the
Company shall be deemed to have discharged the Executive for cause only if any
one of the following conditions existed:

                  (a) If the Executive shall have willfully breached or
         habitually neglected his duties and responsibilities as the Senior Vice
         President of Finance and Administration and Chief Financial Officer of
         the Company; or

                  (b) If the Executive shall have been convicted of any felony
         offense during the term of this Agreement.

The discharge of the Executive by the Company when none of the foregoing
conditions exist shall be deemed to be a discharge without cause.

         11. Resignation for Good Reason. For the purposes of this Agreement,
the Executive shall have resigned for good reason if any one of the following
conditions existed at the time of his resignation:

                  (a) If the Company shall have assigned to the Executive
         authority and responsibilities less significant than, or not comparable
         to, that which he had in his capacity as Senior Vice President of
         Finance and Administration and Chief Financial Officer immediately
         preceding a Change of Control or shall otherwise so limit or restrict
         his authority and responsibilities after a Change of Control;

                  (b) The Company shall have reduced the Executive's annual base
         salary below his annual base salary in effect on the effective date of
         a Change of Control or the Company shall have reduced the Executive's
         annual cash bonus below that of his last annual cash bonus prior to the
         effective date of a Change of Control;


                                       5
<PAGE>   6

                  (c) The Company shall have taken any actions having the
         purpose or intent and the effect of inducing the Executive to resign,
         such as failing to provide the Executive with all personnel benefits
         which are otherwise generally provided to executive officers of the
         Company or reasonably necessary or appropriate for the performance by
         the Executive of his duties as Senior Vice President of Finance and
         Administration and Chief Financial Officer of the Company; or

                  (d) The Company shall have declined to extend the term of this
         Agreement pursuant to Section 6 hereof.

         12. Termination Upon Death. This Agreement shall terminate immediately
upon the date of the death of the Executive.

         13. Remedies. If the Executive shall file any judicial action for
enforcement of this Agreement and successfully recover compensation or damages,
the Executive shall be entitled to recover from the Company an additional amount
equal to interest at ten percent (10%) per annum on the amount recovered from
the date such amount was due and payable together with all expenses and
reasonable attorneys' fees incurred in obtaining legal advice and counselling
respecting his rights under this Agreement and in prosecuting and disposing of
such action. The provisions of this Section shall be cumulative and without
prejudice to any other right or remedy to which the Executive may be entitled
either at law, in equity or under this Agreement and shall not constitute the
exclusive remedy of the Executive for breach of this Agreement.

         14.      General Provisions.

                  (a) Notices. Any notices to be given hereunder by either party
         to the other may be given either by personal delivery in writing or by
         fax, or by mail, registered or certified, postage prepaid, return
         receipt requested, addressed to the parties at their respective
         addresses set forth below their signatures to this Agreement, or at
         such other addresses as they may specify to the other in writing.

                  (b) Law Governing. This Agreement shall be governed by and
         construed in accordance with the laws of the State of Texas.

                  (c) Invalid Provisions. If any provision of this Agreement is
         held to be illegal, invalid or unenforceable under present or future
         laws effective during the term hereof, such provision shall be fully
         severable and this Agreement shall be construed and enforced as if such
         illegal, invalid or unenforceable provision had never comprised a part
         hereof, and the remaining provisions hereof shall remain in full force
         and effect and shall not be affected by the illegal, invalid or
         unenforceable provision or by its severance herefrom. Furthermore, in
         lieu of such illegal, invalid or unenforceable provision, there shall
         be added automatically as part of this Agreement a provision as similar
         in terms to such illegal, invalid or unenforceable provision as may be
         possible and still be legal, valid or enforceable.

                  (d) Entire Agreement. This Agreement sets forth the entire
         understanding of the parties and supersedes all prior agreements or
         understandings, whether written or oral, with respect to the subject
         matter hereof. No terms, conditions or warranties, other than those
         contained herein, and no amendments or modifications hereto shall be
         binding unless made in writing and signed by the parties hereto.


                                       6
<PAGE>   7

                  (e) Binding Effect. This Agreement shall extend to and be
         binding upon and inure to the benefit of the parties hereto, their
         respective heirs, representatives, successors and assigns. All of the
         provisions of this Agreement shall be fully applicable to any successor
         to the Company resulting from a Change of Control. The Company agrees
         that in the event of a tender or exchange offer, merger, consolidation
         or liquidation or any such similar event involving the Company, its
         securities or assets, it shall reveal the existence of this Agreement
         to the acquiring person or entity. The Company further agrees that if
         such action is not inconsistent with the best interests of the Company,
         it shall condition approval of any transactions proposed by the
         acquiror upon obtaining the consent, in writing, of the potential
         successor to the Company to be bound by this Agreement. In the event
         the Executive dies prior to the termination of this Agreement, any
         compensation or other payment due and owing to the Executive on or
         before the date of the Executive's death shall be paid to his estate,
         executors, administrators, heirs or legal representatives. Since the
         duties and services of the Executive hereunder are special, personal
         and unique in nature, the Executive may not transfer, sell or otherwise
         assign his rights, obligations or benefits under this Agreement.

                  (f) Waiver. The waiver by either party hereto of a breach of
         any term or provision of this Agreement shall not operate or be
         construed as a waiver of a subsequent breach of the same provisions by
         either party or of the breach of any other term or provision of this
         Agreement.

                  (g) Titles. Titles of the paragraphs herein are used solely
         for convenience and shall not be used for interpretation or construing
         any word, clause, paragraph or provision of this Agreement.

                  (h) Certain Conflicts. The parties hereto acknowledge and
         agree that Executive has entered into that certain letter agreement
         pertaining to the Executive's employment with the Company dated January
         2, 1998 (the "Letter Agreement"). Where a conflict may arise between
         the provisions of this Agreement and the Letter Agreement, the
         provisions of the Letter Agreement shall apply.

                  (i) Mediation/Arbitration. In the event of a dispute between
         the parties to this agreement, the parties agree to participate in good
         faith in a minimum of four (4) hours of mediation in Dallas, Texas with
         an attorney-mediator trained and certified by the American Arbitration
         Association, the United States Arbitration and Mediation Service, or
         any comparable organization, and to abide by the mediation procedures
         and decision of such organization. The parties agree to equally bear
         the costs of the mediation. In the event the parties cannot resolve
         their dispute through mediation as described herein, the parties agree
         to participate in binding arbitration pursuant to the rules of the
         American Arbitration Association or mutually agreeable similar
         organization. Such arbitration shall be held in Dallas, Texas, shall be
         binding and nonappealable and a judgment on the award to the prevailing
         party (inclusive of reasonable attorney's fees and costs) may be
         entered in any court having competent jurisdiction.


                                       7
<PAGE>   8

         IN WITNESS WHEREOF, the Company and the Executive have executed this
Executive Employment Agreement as of the day and year first written above,
effective as of the date specified above.

                                       COMPANY:

                                       NATIONAL ENERGY GROUP, INC.


                                       By: /s/ MILES D. BENDER
                                          --------------------------------------
                                           Miles D. Bender
                                           President and Chief Executive Officer

                                       4925 Greenville Avenue, Suite 1400
                                       Dallas, Texas 75206
                                       (214) 692-9211
                                       (214) 692-5055 (Fax)


                                       EXECUTIVE:

                                        /s/ FREDERIC R. MILLER
                                       -----------------------------------------
                                       FREDERIC R. MILLER

                                       3701 Atrium Lane
                                       Plano, Texas 75075



                                       8