Document:

<PAGE>

                              SETTLEMENT AGREEMENT

         Charles E. Bayless (the "Employee") and Illinova Corporation (the
"Company") have entered into a "Retention Agreement" dated August 13, 1998. For
greater certainty as to certain compensation, payments, and benefits which may
be provided under the Retention Agreement, and to address certain transition
issues relating to the merger of the Company and Dynegy Inc. (or an affiliate),
the parties to the Retention Agreement wish to enter into this Agreement.
Accordingly, the Employee and the Company agree that, effective December 22,
1999 (the "Effective Date"), the provisions set forth in this Settlement
Agreement will apply:

         1. BENEFITS SCHEDULE. By execution of this Settlement Agreement, the
Employee agrees that the revisions described in Supplement A (the "Benefits
Schedule") which is attached to and forms a part of this Settlement Agreement
shall apply. (For purposes of this Settlement Agreement, the term "Settlement
Agreement" shall include the Benefits Schedule.) The Employee acknowledges that
the amounts payable to the Employee under this Settlement Agreement, and under
the Retention Agreement as modified by this Settlement Agreement, are in excess
of the amounts which would have been payable to the Employee under the Retention
Agreement absent modification by this Settlement Agreement.

         2. ACCELERATION AUTHORIZED. The Employee authorizes the Company to
accelerate, into calendar year 1999, payments that may otherwise have been
payable after 1999 under Company compensation arrangements, including, without
limitation, the Illinova Executive Incentive Compensation Plan, Illinova Long
Term Incentive Compensation Plan, and the Illinova Corporation Supplemental
Pension Plan applicable to the Employee (the "Supplemental Plan"), but not
including the Company's health, life, or disability plans (which would not be
accelerated), in accordance with determinations made by the Company. In
addition, the Company may, in its sole discretion, accelerate severance payments
that may otherwise be due to the Employee upon termination of employment under
any agreement with the Company or any plan or arrangement maintained by the
Company. The Company may, in its discretion, limit the amount accelerated on
behalf of the Employee to the extent it determines that the acceleration would
result in payments that would not be tax deductible by reason of section 162(m)
of the Internal Revenue Code (relating to the $1 million limit on deductible
compensation). If any payment otherwise due (or which may become due) to the
Employee in a later year under the Retention Agreement, this Settlement
Agreement, or any other Company compensation arrangement is accelerated into
1999 under this Settlement Agreement, there shall be a corresponding reduction
in the Company's obligation to make payments to the Employee under that
agreement or arrangement in the later year. As soon as practicable after such
acceleration occurs, the Company will provide the Employee with a schedule of
the amount of the acceleration and the specific compensation, benefits, and
payments that were canceled as a result of the acceleration. Any obligation that
is accelerated under any agreement or arrangement will be subject to a present
value

<PAGE>

adjustment, and any obligation that is accelerated under the Supplemental
Plan will be subject to an actuarial adjustment to reflect such acceleration.

         3. RESTRICTIONS ON ACCELERATION. If approved by the Board of Directors
of the Company, the Company will endeavor to accelerate amounts into calendar
year 1999 so that the Employee's benefits will not be reduced in accordance with
the provisions of section 9 of the Retention Agreement, to the extent that the
Company determines that such amounts would otherwise become due to the Employee
in a later year. However, the Company and the Employee agree that the provisions
of section 9 of the Retention Agreement shall continue to apply, notwithstanding
the provisions of this Settlement Agreement.

         4. GOOD REASON. The Employee acknowledges that (i) entering into this
Settlement Agreement does not constitute a change in compensation, perquisites,
or benefits, does not constitute a cessation of the Employee being employed in
the same or a comparable position (as described in section 2(a)(ii)(C) of the
Retention Agreement), and does not otherwise constitute a basis for "Good
Reason" under the Retention Agreement (as in effect both prior to and after
amendment by this Settlement Agreement), and (ii) the amendment of the Retention
Agreement by this Settlement Agreement constitutes an amendment of the Retention
Agreement that reflects the mutual written agreement of the parties to the
Retention Agreement, and the Employee hereby waives any and all rights to assert
the contrary.

         5. AFFILIATES. For purposes of this Settlement Agreement, the term
"Affiliate" shall mean any "affiliate" of the Company as that term is defined in
Rule 12b-2 under the Securities Exchange Act of 1934.

         6. OTHER COMPENSATION. Except for the covenants and agreements set
forth in this Settlement Agreement, the Employee has received and will receive
no additional compensation or any other type of remuneration from the Company in
consideration of the elections and waivers made pursuant to this Settlement
Agreement. Notwithstanding any provision of this Settlement Agreement or the
Retention Agreement to the contrary, the benefits payable to the Employee under
this Settlement Agreement shall be in lieu of, and not in addition to, any
benefits to which the Employee might otherwise be entitled under any other
severance plan or arrangement maintained by the Company. The acceleration of
compensation under sections 2 and 3 will be disregarded for purposes of the
Illinois Power Company Retirement Income Plan for Salaried Employees, the
Supplemental Plan, and all other plans and arrangements, and will not increase
the Employee's benefits under any such plan or arrangement. The Employee
acknowledges that he or she will have no control over what the Company may do
with the amounts, if any, waived pursuant to this Settlement Agreement.

         7. TAX RETURNS. The Employee agrees to employ PricewaterhouseCoopers to
prepare his or her personal income tax returns for calendar years 1999 and 2000.
The Company will reimburse the Employee for the cost of such preparation.
<PAGE>

         8. RIGHT OF REVOCATION. Except as otherwise provided in this section 8,
this Settlement Agreement will become irrevocable on the Effective Date. If the
Company does not accelerate in accordance with sections 2 and 3, then, for a
period of 14 days following the date written notice is provided to the Employee
(by mailing to the Employee's last residence address indicated in the Company's
records) of the Company's determination not to accelerate, the Employee shall be
entitled to revoke this Settlement Agreement by filing, prior to the 15th day
following provision by the Company of such written notice a written revocation
signed by the Employee stating "I revoke my acceptance of the Settlement
Agreement that became effective December 22, 1999."

Charles E. Bayless

/s/ Charles E. Bayless
-------------------------------

Date: December 22, 1999

                                  Supplement A

                                BENEFITS SCHEDULE

         This Benefits Schedule is attached to and is a part of the Settlement
Agreement between Charles E. Bayless (the "Employee") and Illinova Corporation
(the "Company") dated December 22, 1999, and sets forth certain rights to
compensation, benefits, and payments under the Retention Agreement between the
Employee and the Company dated August 13, 1998 (the "Retention Agreement"). The
Employee and the Company agree that the provisions set forth in this Benefits
Schedule will apply:

A-1.     CHANGE IN CONTROL BENEFITS. The following shall be substituted for the
         portion of section 1 of the Retention Agreement that precedes section
         1(a) of that agreement:

         "CHANGE IN CONTROL BENEFITS. If a Termination Event occurs, then the
         provisions of paragraphs (a), (b), (c), (d), and (e) shall apply:"

A-2.     WELFARE BENEFITS. The following shall be substituted for section 1(d)
         of the Retention Agreement:

         "(d) WELFARE BENEFITS. The Employee and his dependents shall be
         eligible for coverage under the health (including medical and dental)
         plan, life insurance plan, and disability plan (if any) provided to
         full-time employees of Illinois Power Company (or its successor) from
         time to time, subject to the same requirements and limitations as are
         applicable to full-time employees (including, without
<PAGE>

         limitation, any requirement for employee contributions to pay premiums
         for such coverage). Eligibility for each of such health coverage, life
         insurance coverage, and disability coverage, respectively, shall
         continue until the earliest of:

         (i)      The first day the Employee becomes eligible for health
                  coverage, life insurance coverage, or disability coverage,
                  respectively, under a plan or arrangement of the Employee's
                  new employer.

         (ii)     The three-year anniversary of the Employee's Termination
                  Event.

         (iii)    The date the Employee attains age 65.

         Medical coverage provided under this section 1(d) shall be counted
         towards the Company's obligation to provide coverage under the
         provisions of section 4980B of the Internal Revenue Code and section
         601 of the Employee Retirement Income Security Act (sometimes referred
         to as "COBRA coverage").

         The Employee and his or her dependents, if any, shall be eligible to
         participate in any benefit plans of the Company which provide health
         and life or similar benefits coverage as are then extended to employees
         of the Company electing early retirement at age 55 on the same terms
         and subject to the same conditions as are applicable to such employees;
         provided that such coverage shall not be furnished if the Employee
         waives coverage by giving written notice of waiver to the Company.
         Nothing in the Settlement Agreement (including this Benefits Schedule)
         shall be construed to limit the right which the Company otherwise has
         to amend or termination any health, life or other plan covering the
         Company's employees (or their dependents).

A-3.     GRANT OF STOCK. By action of the Board of Directors of the Company on
         December 9, 1998, the Employee was granted the right to receive 6,000
         shares of the Company's common stock ("Stock") subject to certain
         conditions. It is agreed by the parties that the distributions provided
         under this section A-3 are in full settlement of the Employee's rights
         under that grant.

         (a) The Company granted to the Employee 4,000 shares of the Company's
         common stock ("Stock") on December 9, 1999. These 4,000 shares of Stock
         shall be delivered to the Employee as soon as practicable on or after
         that date.

         (b) The Employee was granted 2,000 shares of Stock on December 9, 1998
         granted to the Employee at the December 9, 1998 Board of Directors
         meeting, with delivery of such shares to be made in the future. Since
         that date, stock units representing the 2,000 shares have been credited
         to a book account maintained by the Company. As of each dividend record
         date for the Stock following December 9, 1998 and prior to December 9,
         1999, the account has been credited with additional stock units
         (including fractional stock units) equal to (i) the amount of
<PAGE>

         the dividend that would be payable with respect to the number of
         shares of Stock equal to the number of stock units credited to the
         account on the dividend record date; divided by (ii) the fair
         market value of a share of Stock on the date of payment of the
         dividend.

         (c) As soon as practicable after December 9, 1999, the Company will
         distribute to the Employee the sum of 4,000 shares granted in
         accordance with paragraph (a) above, and the number of shares equal to
         the number of share units that, as of December 9, 1999, are credited to
         the account described in paragraph (b) next above, and the Employee
         shall be fully vested in all such shares as of December 9, 1999.

A-4.     LONG-TERM INCENTIVE PAYMENT. If (i) the Employee is employed through
         December 31, 1999; (ii) the Employee's employment is terminated prior
         to that date by the Company without Good Cause (as defined in the
         Retention Agreement); or (iii) the Employee resigns as an employee of
         the Company and becomes a consultant to the Company in accordance with
         section A-6, then the Company shall provide the Employee with an award
         for each of the three performance periods currently in effect (January
         1, 1999 through December 31, 1999; January 1, 1999 through December 31,
         2000; and January 1, 1999 through December 31, 2001). The determination
         of the performance for the periods will be determined near the end of
         1999, and will be equal to the performance figures available as of the
         date of such determination, with such performance deemed to have
         continued through the end of the performance periods, as determined by
         the Compensation Committee of the Board of Directors of the Company.
         The amount of the benefit payable under this section A-4 to the
         Employee for each of these performance periods shall be equal to the
         amount that would be payable on such performance for the entire period,
         but subject to a pro-rata reduction to reflect the portion of the
         performance period after December 31, 1999, in accordance with the
         following schedule:

<TABLE>
<CAPTION>
--------------------------------------------------------------------------------------------------------------------
               For the Performance Period:                    The following percent of the total award that is
                                                               determined to be payable by the Company for the
                                                                        Performance Period shall be:
--------------------------------------------------------------------------------------------------------------------
<S>                                                                                 <C>
        January 1, 1999 through December 31, 1999                                   100%
--------------------------------------------------------------------------------------------------------------------
        January 1, 1999 through December 31, 2000                                    50%
--------------------------------------------------------------------------------------------------------------------
        January 1, 1999 through December 31, 2001                                    33%
--------------------------------------------------------------------------------------------------------------------
</TABLE>

         Except as provided in this section A-4, the Employee shall not be
         entitled to any amounts with respect to the Long-Term Incentive Plan
         for any period.

A-5.     COMPENSATION CESSATION. Except as otherwise specifically provided in
         this Settlement Agreement, or the provisions of Retention Agreement
         (excluding
<PAGE>

         section 1(d) as in effect prior to amendment by this Settlement
         Agreement), the Employee shall not be eligible for any compensation
         or benefits for periods after the Employee's date of termination.
         Except as otherwise provided in section A-6, nothing in this
         Settlement Agreement or the Retention Agreement shall be construed
         to give the Employee any right to be reemployed or otherwise
         retained by the Company or an Affiliate after such termination of
         employment. However, the Employee, if reemployed, shall be eligible
         for such compensation and benefits, and shall be eligible for
         participation in such benefit plans and arrangements, with respect
         to any such reemployment as may be agreed upon by the Employee and
         the employer, and shall be subject to the terms that may be
         applicable to the Employee under any such plan or arrangement.

A-6.     CONSULTING. The Company and the Employee agree to enter into a
         consulting relationship subject to the following:

         (a) The Employee agrees that, at the request of the Company, he will
         resign as an officer and employee of the Company, and after the
         effective date of such resignation (which will be determined by the
         Company), he will serve in the role of a consultant to the Company with
         respect to transition issues relating to the merger of the Company and
         Dynegy Inc. or an affiliate.

         (b) The Employee shall provide such consulting services during the
         period (the "Consulting Period") specified by the Company, provided
         that the period may not end prior to the day following the occurrence
         of a Change in Control (as defined in the Retention Agreement), and may
         not extend beyond January 31, 2000 without the consent of the Employee.
         During the Consulting Period, the Employee shall be required to provide
         up to 80 hours of consulting services (as requested by the President of
         the Company), shall be entitled to payment of $10,000 (regardless of
         the number of hours of service provided during the period), and shall
         also be reimbursed for his expenses incurred in connection with his
         responsibilities for the Company. During the period he serves as a
         consultant, the Employee shall not be treated as an employee of the
         Company, and, except as provided in this paragraph (b), he shall not be
         entitled to receive compensation or benefits provided to the Company's
         employees.

         (c) It is understood by the parties that the arrangement described in
         this section A-6 is expected to facilitate the transition and provide
         other material benefits to the Company, but is not intended to
         adversely affect the Employee's rights to the separation benefits to
         which he would otherwise be entitled. Accordingly, for purposes of the
         following, the Employee's employment with the Company shall not be
         deemed to have terminated during the period in which he is engaged as a
         consultant to the Company in accordance with this section A-6, but such
         employment will be deemed to have been terminated by the Company
         without Good Cause on the date he ceases to be so engaged as a
         consultant to the Company:
<PAGE>

         (i)      The Employee's right to receive Change in Control Benefits
                  under section 1 of the Retention Agreement, including, without
                  limitation, the determination of the date of a Termination
                  Event. However, the Employee waives any and all rights to
                  assert the existence of "Good Reason" pursuant to 2(a)(ii)(A)
                  (relating to salary reduction), 2(a)(ii)(B) (relating to
                  reduction of vacation, fringe benefits, or perquisites), or
                  2(a)(ii)(C) (relating to retaining a comparable position) with
                  respect to his resignation as an officer and employee and
                  acceptance of his role as a consultant, and with respect to
                  the circumstances of his serving as a consultant. If the
                  Employee serves as a consultant to the Company, then, when he
                  ceases to serve as a consultant and becomes entitled to Change
                  in Control Benefits in accordance with section 1(a) of the
                  Retention Agreement, and notwithstanding the terms of the
                  Retention Agreement with respect to the determination of such
                  amount, his "latest bonus" as described in section 1(a)(II) of
                  the Retention Agreement shall be deemed to be $431,250.00.

         (ii)     The Employee's rights and obligations under the terms of the
                  promissory note and tax letter. For purposes of this paragraph
                  (ii), the term "promissory note" shall mean the promissory
                  note dated August 13, 1998 with respect to the borrowing of
                  $500,000 by the Employee from the Company, and the term "tax
                  letter" shall mean the letter from the Company to the Employee
                  dated August 13, 1998 providing for the tax gross-up with
                  respect to the forgiveness of interest under the promissory
                  note.

         (iii)    The Employee's right to receive benefits under the
                  Supplemental Pension Plan, including, without limitation, the
                  Employee's right to receive the Accrued Vested Benefit under
                  the Supplemental Pension Plan in accordance with section 1(c)
                  of the Retention Agreement. If the Employee serves as a
                  consultant to the Company, then, when he becomes entitled to
                  benefits in accordance under the Supplemental Pension Plan,
                  and notwithstanding the terms of the plan with respect to the
                  determination of such amount, the amount of the Employee's
                  Final Average Earnings shall be $804,542.00

(iv)  The Employee's right to hold, vest in, and exercise any stock options
granted to him by the Company. These options shall expire January 30, 2005. To
the extent not already vested, stock options shall vest in accordance with
Section Three of the Non-Qualified Stock Option Agreement between the Company
and the Employee dated June 24, 1998. Upon the merger among Dynegy Inc., the
Company, and their affiliates, the right to purchase shares of the Company under
such options shall be replaced with the right to purchase a corresponding number
of shares of Dynegy Inc. (based on the exchange rate for other holders of
options to purchase shares of Stock of the Company). The portion of the options
to purchase Stock of the Company that have been granted to

<PAGE>

the Employee which provide for exercisability upon the attainment of a $35
per share and $40 per share of the Company's Stock shall, upon consummation
of the merger among Dynegy Inc., the Company, and their affiliates, be
replaced respectively with a $35 per share and $40 per share price level
requirement based on the shares of Dynegy Inc.<PAGE>

                                                               November 29, 1999

                              SETTLEMENT AGREEMENT

         George W. Miraben (the "Employee") and Illinova Corporation (the
"Company") have entered into a "Retention Agreement" dated January 18, 1999. For
greater certainty as to certain compensation, payments, and benefits which may
be provided under the Retention Agreement, the parties to the Retention
Agreement wish to specifically identify such compensation, payments, and
benefits at this time. Accordingly, the Employee and the Company agree that,
effective December 6, 1999 (the "Effective Date"), the terms of this Settlement
Agreement will apply, and the current section 1 of the Retention Agreement shall
be without effect:

         1. SUBSTITUTE PAYMENT PROVISIONS. The Employee agrees that the
compensation, payments, and benefits as described in Supplement A (the "Benefits
Schedule") which is attached to and forms a part of this Settlement Agreement
are in lieu of any and all compensation, payments, and benefits under section 1
of the Retention Agreement. (For purposes of this Settlement Agreement, the term
"Settlement Agreement" shall include the Benefits Schedule.) By execution of
this Settlement Agreement, the Employee waives any and all rights to the amounts
that would have been payable under section 1 of the Retention Agreement absent
this Settlement Agreement. The Employee acknowledges that the amounts payable to
the Employee under this Settlement Agreement, and under the Retention Agreement
as modified by this Settlement Agreement, are in excess of the amounts which
would have been payable to the Employee under the Retention Agreement absent
modification by this Settlement Agreement.

         2. ACCELERATION AUTHORIZED. The Employee authorizes the Company to
accelerate, into calendar year 1999, payments that may otherwise have been
payable after 1999 under Company compensation arrangements, including, without
limitation, the Illinova Executive Incentive Compensation Plan, Illinova Long
Term Incentive Compensation Plan, and the Illinova Corporation Supplemental
Pension Plan applicable to the Employee (the "Supplemental Plan"), but not
including the Company's health, life, or disability plans (which would not be
accelerated), in accordance with determinations made by the Company. In
addition, the Company may, in its sole discretion, accelerate severance payments
that may otherwise be due to the Employee upon termination of employment under
any agreement with the Company or any plan or arrangement maintained by the
Company. The Company may, in its discretion, limit the amount accelerated on
behalf of the Employee to the extent it determines that the acceleration would
result in payments that would not be tax deductible by reason of section 162(m)
of the Internal Revenue Code (relating to the $1 million limit on deductible
compensation). If any payment otherwise due (or which may become due) to the
Employee in a later year under the Retention Agreement, this Settlement
Agreement, or any other Company compensation arrangement is accelerated into
1999 under this Settlement Agreement, there shall be a corresponding reduction
in the Company's obligation to make payments
<PAGE>

to the Employee under that agreement or arrangement in the later year. As
soon as practicable after such acceleration occurs, the Company will provide
the Employee with a schedule of the amount of the acceleration and the
specific compensation, benefits, and payments that were canceled as a result
of the acceleration. Any obligation that is accelerated under any agreement
or arrangement will be subject to a present value adjustment, and any
obligation that is accelerated under the Supplemental Plan will be subject to
an actuarial adjustment to reflect such acceleration.

         3. RESTRICTIONS ON ACCELERATION. If approved by the Board of Directors
of the Company, the Company will endeavor to accelerate amounts into calendar
year 1999 so that the Employee's benefits will not be reduced in accordance with
the provisions of section 9 of the Retention Agreement, to the extent that the
Company determines that such amounts would otherwise become due to the Employee
in a later year. However, the Company and the Employee agree that the provisions
of section 9 of the Retention Agreement shall continue to apply, notwithstanding
the provisions of this Settlement Agreement.

         4. GOOD REASON. The Employee acknowledges that (i) entering into this
Settlement Agreement does not constitute a change in compensation, perquisites,
or benefits, does not constitute a change in the nature or scope of the
Employee's authority, and does not otherwise constitute a basis for "Good
Reason" under the Retention Agreement (as in effect both prior to and after
amendment by this Settlement Agreement), and (ii) the amendment of the Retention
Agreement by this Settlement Agreement does not constitute an amendment of the
Retention Agreement (as in effect both prior to and after amendment by this
Settlement Agreement) by the Company that adversely affects the Employee's
rights under the Retention Agreement, and hereby waives any and all rights to
assert the contrary.

         5. OTHER EMPLOYMENT. The Employee shall not be required to mitigate
damages by seeking other employment or otherwise. Except as specifically
provided in section A-1(b) of the Benefits Schedule with respect to termination
of health coverage, life insurance coverage, and disability coverage upon the
Employee's coverage under a plan or arrangement of the Employee's employer, the
Company's obligations under this Settlement Agreement shall not be reduced in
any way by reason of any compensation received by the Employee from sources
other than the Company or the Affiliates after termination of Employee's
employment with the Company. For purposes of this Settlement Agreement, the term
"Affiliate" shall mean any "affiliate" of the Company as that term is defined in
Rule 12b-2 under the Securities Exchange Act of 1934.

         6. OTHER COMPENSATION. Except for the covenants and agreements set
forth in this Settlement Agreement, the Employee has received and will receive
no additional compensation or any other type of remuneration from the Company in
consideration of the elections and waivers made pursuant to this Settlement
Agreement. Notwithstanding any provision of this Settlement Agreement or the
Retention Agreement to the contrary, the benefits payable to the Employee under
this Settlement Agreement shall be in lieu of,
<PAGE>

and not in addition to, any benefits to which the Employee might otherwise be
entitled under any other severance plan or arrangement maintained by the
Company. The acceleration of compensation under sections 2 and 3 will be
disregarded for purposes of the Illinois Power Company Retirement Income Plan
for Salaried Employees, the Supplemental Plan, and all other plans and
arrangements, and will not increase the Employee's benefits under any such
plan or arrangement. The Employee acknowledges that he or she will have no
control over what the Company may do with the amounts, if any, waived
pursuant to this Settlement Agreement.

         7. TAX RETURNS. The Employee agrees to employ PricewaterhouseCoopers to
prepare his or her personal income tax returns for calendar years 1999 and 2000.
The Company will reimburse the Employee for the cost of such preparation.

         8.  RIGHT OF REVOCATION.

(a)      The Employee may revoke this Settlement Agreement by filing, prior to
         the Effective Date, with Kim B. Leftwich, Vice President, a written
         revocation signed by the Employee stating "I revoke my acceptance of
         the Settlement Agreement that would otherwise become effective December
         6, 1999." Unless the Employee has revoked this Settlement Agreement by
         the Effective Date, and except as otherwise provided in section 8(b),
         this Settlement Agreement will become irrevocable on the Effective
         Date.

(b)      If the Company does not accelerate in accordance with sections 2 and 3,
         then, for a period of 14 days following the date written notice is
         provided to the Employee (by mailing to the Employee's last residence
         address indicated in the Company's records) of the Company's
         determination not to accelerate, the Employee shall be entitled to
         revoke this Settlement Agreement by filing, prior to the 15th day
         following provision by the Company of such written notice a written
         revocation signed by the Employee stating "I revoke my acceptance of
         the Settlement Agreement that became effective December 6, 1999."

  /s/ GW Miraben               George W. Miraben                  12/3/99
------------------           ---------------------               ---------
     SIGNATURE                    PRINT NAME                       DATE

THIS FORM MUST BE RETURNED TO THE ILLINOIS POWER COMPANY, KIM B. LEFTWICH, VICE
PRESIDENT, AT 500 SOUTH 27 STREET, DECATUR, ILLINOIS 62521, BY 5:00 P.M. ON
DECEMBER 6, 1999 AND SHALL BECOME IRREVOCABLE AT THAT TIME.
<PAGE>

                                  Supplement A

                                BENEFITS SCHEDULE

         This Benefits Schedule is attached to and is a part of the Settlement
Agreement between George W. Miraben (the "Employee") and Illinova Corporation
(the "Company") dated November 29, 1999, and sets forth certain rights to
compensation, benefits, and payments under the Retention Agreement between the
Employee and the Company dated January 18, 1999 (the "Retention Agreement"). The
compensation, benefits, and payments under the Settlement Agreement (including
this Benefits Schedule) shall be in lieu of any compensation, benefits,
payments, or rights that would otherwise be provided under section 1 of the
Retention Agreement in the absence of this Settlement Agreement.

A-1.     SEVERANCE BENEFITS.  If a Termination Event (as defined in the
         Retention Agreement) occurs, the Employee shall be entitled to the
         Severance Benefits described in this section A-1:

         (a) LUMP SUM PAYMENT. The Company shall, within 30 days after a
         Termination Event, make a lump sum cash payment to the Employee equal
         to the sum of:

         (i)      thirty-six (36) months' salary at the greater of (I) the
                  Employee's salary rate in effect on the date of the Change in
                  Control, or (II) the Employee's salary rate in effect on the
                  date Employee's employment with the Company terminates; PLUS

         (ii)     three times the amount of the Employee's annual award under
                  the Illinova Executive Incentive Compensation Plan for
                  calendar year 1999 (which ordinarily would be paid in March,
                  2000, but may be paid in December 1999).

         (b) WELFARE PLAN CONTINUATION. The Employee and his or her dependents
         shall be eligible for coverage under the health (including medical and
         dental) plan, life insurance plan, and disability plan (if any)
         provided to full-time employees of Illinois Power Company (or its
         successor) from time to time, subject to the same requirements and
         limitations as are applicable to full-time employees (including,
         without limitation, any requirement for employee contributions to pay
         premiums for such coverage). Eligibility for each of such health
         coverage, life insurance coverage, and disability coverage,
         respectively, shall continue until the earliest of:

         (i)      The first day the Employee becomes eligible for health
                  coverage, life insurance coverage, or disability coverage,
                  respectively, under a plan or arrangement of the Employee's
                  new employer.

         (ii)     In the case of health coverage and life insurance coverage, if
                  the Employee has attained age 50 but has not attained age 52
                  on the date of termination,
<PAGE>

                  the Employee's 55th birthday; and if the Employee has not
                  attained age 50, or is older than age 52 on the date of
                  termination, the three-year anniversary of the Employee's
                  Termination Event. In the case of disability coverage, the
                  three-year anniversary of the Employee's Termination Event.

         (iii) The date the Employee attains age 65.

         Medical coverage provided under this section A-1(b) shall be counted
         towards the Company's obligation to provide coverage under the
         provisions of section 4980B of the Internal Revenue Code and section
         601 of the Employee Retirement Income Security Act (sometimes referred
         to as "COBRA coverage").

         (c) RETIREE WELFARE BENEFITS. If, either: (a) the Employee has attained
         age 50 but has not attained age 55 on the date of termination of
         employment, and the Employee's medical and life coverage under section
         A-1(b) of this Benefits Schedule are continued until the Employee
         attains age 55, or (b) the Employee has attained age 55 on or before
         the date of termination of employment, then the Employee and his or her
         dependents, if any, shall be eligible to participate in any benefit
         plans of the Company which provide health and life or similar benefits
         coverage as are then extended to employees of the Company electing
         early retirement at age 55 on the same terms and subject to the same
         conditions as are applicable to such employees; provided that such
         coverage shall not be furnished if the Employee waives coverage by
         giving written notice of waiver to the Company. Nothing in the
         Settlement Agreement (including this Benefits Schedule) shall be
         construed to limit the right which the Company otherwise has to amend
         or termination any health, life or other plan covering the Company's
         employees (or their dependents).

         (d) PROMISSORY NOTE. Notwithstanding any provision in the promissory
         note or the tax letter to the contrary, any obligation of the Employee
         for payment of principal and interest otherwise due under the
         promissory note shall be forgiven, and the Employee shall be entitled
         to the tax gross-up payment as described in the tax letter with respect
         to such forgiven interest (but not with respect to the forgiven
         principal). For purposes of this paragraph (d), the term "promissory
         note" shall mean the promissory note dated January 18, 1999 with
         respect to the borrowing of $250,000 by the Employee from the Company,
         and the term "tax letter" shall mean the letter from the Company to the
         Employee dated January 18, 1999 providing for the tax gross-up with
         respect to the forgiveness of interest under the promissory note.

         (e) SUPPLEMENTAL PENSION. Notwithstanding any provision in the
         Supplemental Pension Plan to the contrary, the Employee's Accrued
         Vested Benefit under the Supplemental Pension Plan shall be equal to
         40% of the Employee's Final Average Earnings (as defined under the
         Supplemental Pension Plan) as of the date of his termination of
         employment with the Company.
<PAGE>

         (f) OPTION EXERCISE PERIOD. Notwithstanding any provision of the
         applicable stock option agreement to the contrary, any stock option or
         portion thereof that is exercisable on the date of the Employee's
         Termination Event (as that term is used in the Retention Agreement)
         shall not be forfeited on the date of such Termination Event, but shall
         instead remain exercisable for the one-year period following the
         Termination Event; provided that, in no event shall such the option be
         exercisable after the date on which the option would otherwise expire
         if the Employee had continued in the employ of the Company.

         (g) OPTION VESTING. If the Employee is employed by the Company on the
         date of a Change in Control then, with respect to any stock option
         granted to the Employee by the Company prior to the Change in Control
         that is outstanding on the date of the Change in Control, that option
         shall be exercisable on and after the date of the Change in Control.
         Except as otherwise provided in the preceding sentence with respect to
         exercisability of options, the options shall remain subject to the
         expiration provisions and other terms of the option awards without
         regard to the preceding sentence; and the preceding sentence shall not
         apply to any stock option to the extent that the terms governing such
         option expressly reference this Agreement and expressly provide that
         the provisions of such sentence are inapplicable.

A-2.     LONG-TERM INCENTIVE PAYMENT. If the Employee is employed through
         December 31, 1999 or the Employee's employment is terminated prior to
         that date by the Company without Cause (as defined in the Retention
         Agreement), and if the Employee is participating in the Illinova Long
         Term Incentive Compensation Plan (the "Long-Term Incentive Plan"), the
         Company shall provide the Employee with an award for each of the three
         performance periods currently in effect (January 1, 1999 through
         December 31, 1999; January 1, 1999 through December 31, 2000; and
         January 1, 1999 through December 31, 2001). The determination of the
         performance for the periods will be determined near the end of 1999,
         and will be equal to the performance figures available as of the date
         of such determination, with such performance deemed to have continued
         through the end of the performance periods, as determined by the
         Compensation Committee of the Board of Directors of the Company. The
         amount of the benefit payable under this section A-2 to the Employee
         for each of these performance periods shall be equal to the amount that
         would be payable on such performance for the entire period, but subject
         to a pro-rata reduction to reflect the portion of the performance
         period after December 31, 1999, in accordance with the following
         schedule:

<TABLE>
<CAPTION>
--------------------------------------------------------------------------------------------------------------------
               For the Performance Period:                    The following percent of the total award that is
                                                               determined to be payable by the Company for the
                                                                        Performance Period shall be:
--------------------------------------------------------------------------------------------------------------------
<S>                                                                                 <C>
        January 1, 1999 through December 31, 1999                                   100%
--------------------------------------------------------------------------------------------------------------------
<PAGE>

--------------------------------------------------------------------------------------------------------------------
        January 1, 1999 through December 31, 2000                                    50%
--------------------------------------------------------------------------------------------------------------------
        January 1, 1999 through December 31, 2001                                    33%
--------------------------------------------------------------------------------------------------------------------
</TABLE>

         Except as provided in this section A-2, the Employee shall not be
         entitled to any amounts with respect to the Long-Term Incentive Plan
         for any period.

A-3. COMPENSATION CESSATION. Except as otherwise specifically provided in this
Settlement Agreement, or the provisions of Retention Agreement (excluding
section 1 as in effect prior to amendment by this Settlement Agreement), the
Employee shall not be eligible for any compensation or benefits for periods
after the Employee's date of termination. Nothing in this Settlement Agreement
or the Retention Plan shall be construed to give the Employee any right to be
reemployed by the Company or an Affiliate after such termination of employment.
However, the Employee, if reemployed, shall be eligible for such compensation
and benefits, and shall be eligible for participation in such benefit plans and
arrangements, with respect to any such reemployment as may be agreed upon by the
Employee and the employer, and shall be subject to the terms that may be
applicable to the Employee under any such plan or arrangement.

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