Document:

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                                                                  Exhibit 10.104

                          MIDWEST LESSOR LEASE GUARANTY

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                          MIDWEST LESSOR LEASE GUARANTY
                                      (T1)

                          Dated as of December 15, 1999

                                     made by

                             MIDWEST GENERATION, LLC
                                  as Guarantor

                                 Collins Station
                 Fossil Fuel-Fired Electric Generating Facility

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                          MIDWEST LESSOR LEASE GUARANTY
                                      (T1)

        This MIDWEST LESSOR LEASE GUARANTY (this "Guaranty"), dated as of
December 15, 1999, is issued by MIDWEST GENERATION, LLC, a Delaware limited
liability company, as guarantor (the "Guarantor") in favor of the Beneficiary
(as defined in Section 4 below).

                                   WITNESSETH:

        WHEREAS, the Guarantor is an affiliate of Collins Holdings EME, LLC, a
Delaware Limited liability company ("Collins Holdings").

        WHEREAS, simultaneously herewith Collins Holdings is entering into a
Participation Agreement (T1), dated as of December 15, 1999 (the "PARTICIPATION
AGREEMENT"), with the Collins Trust I (the "Owner Lessor"), Collins Generation
I, LLC (the "OWNER PARTICIPANT") Wilmington Trust Company, not in its individual
capacity, except as expressly provided therein, but only as owner trustee (the
"OWNER TRUSTEE"), Edison Mission Midwest Holdings Co., the Guarantor, Midwest
Funding LLC, as lender, Bayerische Landesbank International S.A., as issuer of
the Midwest Letter of Credit, Bayerische Landesbank Girozentrale, as issuer of
the RCE Letter of Credit and Citibank, N.A., as Holder Representative;

        WHEREAS, Collins Holdings intends to enter into a Facility Lease
Agreement (T1) dated as of December 15, 1999 (the "Facility Lease") with the
Beneficiary;

        WHEREAS, Collins Holdings intends to enter into a Facility Site Sublease
Agreement (T1), dated as of December 15, 1999 (the "Facility Site Sublease")
with the Beneficiary;

        WHEREAS, Collins Holdings intends to enter into a Facility Site
Sub-Sub-Lease Agreement (T1), dated as of December 15, 1999 (the "Facility Site
Sub-Sublease) with the Guarantor and the Beneficiary;

        WHEREAS, it is a condition precedent to the parties' obligations under
the Participation Agreement that the Guarantor enter into and deliver this
Guaranty; and

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        WHEREAS, the Guarantor anticipates benefitting directly and indirectly
from the transactions contemplated by the Participation Agreement, the Facility
Lease, the Facility Site Sublease and the Facility Site Sub-Sublease and is
executing and delivering this Guaranty to induce the Beneficiary to enter into
the Participation Agreement, the Facility Lease, the Facility Site Sublease and
the Facility Site Sub-Sublease.

        NOW, THEREFORE, in consideration of the foregoing and other benefits
accruing to the Guarantor, the receipt and sufficiency of which are hereby
acknowledged, the Guarantor agrees as follows:

SECTION 1.     DEFINITIONS

        For purposes of this Guaranty, capitalized terms used but not otherwise
defined herein shall have the respective meanings specified in Appendix A to the
Participation Agreement. The general provisions of Appendix A shall apply to
terms used in this Guaranty and specifically defined herein. Any term defined by
reference to an agreement, instrument or other document shall have the meaning
so assigned to it whether or not such document is in effect.

SECTION 2.     COVENANTS

        SECTION 2.1 Subject to the terms hereof, the Guarantor hereby
unconditionally and irrevocably guarantees, as primary obligor and not merely as
a surety, to the Beneficiary (a) the due, complete and punctual performance and
observance by Collins Holdings of each term, provision and condition binding
upon Collins Holdings pursuant to any of the Operative Documents to which
Collins Holdings is or becomes a party (the "CHE OPERATIVE DOCUMENTS") and (b)
the due, punctual and full payment (when and as the same may become due and
payable) of each amount that Collins Holdings is or may become obligated to pay
under or pursuant to any of the CHE Operative Documents, in accordance with the
terms thereof, by acceleration or otherwise without offset or deduction.

        SECTION 2.2 In the case of any failure by Collins Holdings to perform
and observe any such term, provision or condition after notice thereof by the
Beneficiary, the Guarantor agrees to cause such performance or observance to be
done, and in the case of any failure by Collins Holdings to make such payment as
and when the same shall become due and payable (by acceleration or otherwise),
the Guarantor hereby

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agrees to make such payment (and, in addition, such further amounts, if any,
as shall be sufficient to cover the costs and expenses of collection
hereunder); PROVIDED, nothing herein shall expand the aforesaid obligations
of the Guarantor beyond those of Collins Holdings under any of the CHE
Operative Documents.
     All such obligations and indebtedness set forth in Section 2.1 hereof and
this Section 2.2 are referred to in this Guaranty as the "OBLIGATIONS."

        SECTION 2.3 This Guaranty is a direct, independent and primary
obligation of the Guarantor and is an irrevocable, absolute, present,
unconditional and continuing obligation and guarantee of payment and performance
(and not merely of collection) and the validity and enforceability of this
Guaranty shall be absolute and is not conditioned in any way upon (a) the
institution of suit or the taking of any other action or any attempt to enforce
performance of or compliance with the obligations, covenants or undertakings
(including any payment obligations) of Collins Holdings, other than providing
notice to Collins Holdings, (b) the genuineness, validity, legality or
enforceability of any of the CHE Operative Documents or the lack of power or
authority of Collins Holdings to enter into any of the CHE Operative Documents
or any substitution, release or exchange of any other guaranty or any other
security for any of the Obligations or any other circumstance whatsoever (other
than payment or performance) that might otherwise constitute a legal or
equitable discharge or defense of a surety or guarantor, (c) any right of
set-off, recoupment or counterclaim, (d) any attempt to collect from Collins
Holdings or any other entity or to perfect or enforce any security or any other
condition or contingency or (e) any other action, occurrence or circumstance
whatsoever.

        SECTION 2.4 Without limiting the generality of the foregoing, the
Guarantor shall have no right to terminate this Guaranty, or to be released,
relieved or discharged from its obligations hereunder, and such obligations
shall be neither affected nor diminished for any reason whatsoever, including:

                      (i) any amendment or supplement to or modification of any
                      of the CHE Operative Documents, any extension or renewal
                      of Collins Holdings' obligations under any CHE Operative
                      Document, or any subletting, assignment or transfer of
                      Collins Holdings' or the Beneficiary's interest in the CHE
                      Operative Documents;

                      (ii) any bankruptcy, insolvency, readjustment,
                      composition, liquidation or any other change in the legal
                      status of Collins Holdings or any

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                      rejection or modification of the Obligations of Collins
                      Holdings or the Beneficiary as a result of any bankruptcy,
                      reorganization, insolvency or similar proceeding;

                      (iii) any furnishing or acceptance of additional security
                      or any exchange, substitution, surrender or release of
                      any security;

                      (iv) any waiver, consent or other action or inaction or
                      any exercise or nonexercise of any right, remedy or power
                      with respect to the Obligations or any of the CHE
                      Operative Documents;

                      (v) the unenforceability, lack of genuineness or
                      invalidity of the Obligations or any part thereof or the
                      unenforceability, lack of genuineness or invalidity of any
                      agreement relating thereto;

                      (vi) (A) any merger or consolidation of Collins Holdings
                      or the Guarantor into or with any other Person, (B) any
                      change in the structure of Collins Holdings, (C) any
                      change in the ownership of Collins Holdings or the
                      Guarantor or (D) any sale, lease or transfer of any or all
                      of the assets of Collins Holdings or the Guarantor to any
                      other Person;

                      (vii) any default, misrepresentation, negligence,
                      misconduct or other action or inaction of any kind by the
                      Beneficiary under or in connection with any CHE Operative
                      Document or any other agreement relating to this Guaranty,
                      except to the extent that any such default,
                      misrepresentation, negligence, misconduct or other action
                      or inaction would limit the Obligations; or

                      (viii) any other circumstance whatsoever (except the
                      complete payment and performance of the Obligations),
                      including, without limitation, any act or omission of
                      Collins Holdings or the Beneficiary which changes the
                      scope of the Guarantor's risk.

        SECTION 2.5 The Guarantor hereby unconditionally waives and releases, to
the extent permitted by law promptness, diligence and notice as to the
Obligations guaranteed hereby and acceptance of this Guaranty, and waives any
other circumstance which might otherwise constitute a defense available to, or a
discharge of, the

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Guarantor, including, without limitation, notice of default or any failure on
the part of Collins Holdings to perform and comply with any Obligation and
agrees that, except as otherwise provided herein, it shall not be required to
consent to or receive any notice of any amendment or modification of, or
waiver, consent or extension with respect to, the CHE Operative Documents. No
failure to exercise and no delay in exercising, on the part of the
Beneficiary, any right, power or privilege hereunder shall operate as a
waiver thereof, nor shall any single or partial exercise of any right, power
or privilege preclude any other or further exercise thereof, or the exercise
of any other power or right. The rights and remedies herein provided are
cumulative and not exclusive of any rights or remedies provided by law.

        SECTION 2.6 The Guarantor agrees to pay any costs and expenses incurred
by the other parties to the Participation Agreement in connection with the
enforcement of this Guaranty.

SECTION 3.     GUARANTOR'S REPRESENTATIONS, WARRANTIES AND AGREEMENTS

               In order to induce the Beneficiary to enter into the
Participation Agreement, the Facility Lease, the Facility Site Sub-lease, the
Facility Site Sub-Sublease, the Guarantor represents and warrants unto the
Beneficiary as set forth in this Section III.

        SECTION 3.1 The Guarantor is duly organized, validly existing and in
good standing under the laws of the state of incorporation and has full power,
authority and legal right to execute, deliver and perform this Guaranty.

        SECTION 3.2 The execution, delivery and performance by the Guarantor of
this Guaranty has been duly authorized by all necessary corporate action. This
Guaranty constitutes a legal, valid and binding obligation of the Guarantor
enforceable against the Guarantor in accordance with its terms, except as such
enforcement may be affected by applicable bankruptcy, insolvency, moratorium and
other similar laws affecting creditors' rights generally.

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SECTION 4.     BENEFICIARY

        The Owner Lessor, together with its affiliates, successors, assigns,
agents, members, partners, directors, officers or employees, is the beneficiary
of this Guaranty (the "BENEFICIARY"). The Guarantor acknowledges and consents to
the assignment of this Guaranty by the Owner Lessor to the Holder Representative
(for the benefit of the Holders). The Guarantor further acknowledges and
consents to any subsequent assignments of this Guaranty by the Holders or the
Holder Representative. The Owner Lessor hereby irrevocably directs (it being
understood and agreed that such direction shall be deemed to have been revoked
after the Lien over the Lessor Collateral created under the Lessor Security
Documents shall have been fully discharged in accordance with its terms) the
Guarantor, and the Guarantor agrees, to make all payments to be made to the
Owner Lessor pursuant to Section 2.1 or 2.2 to the Holder Representative for
deposit in the Holder Representative's Account. The Guarantor agrees that the
Holder Representative (acting for the benefit of the Holders) and any assignee
thereof shall be entitled to exercise any and all rights of the Owner Lessor
under this Guaranty in accordance with the terms hereof (in its name or in the
name of the Owner Lessor), and the Guarantor shall comply in all respects with
such exercise. Without limiting the generality of the foregoing, the Holder
Representative and any assignee thereof shall have the full right and power to
enforce directly against the Guarantor all obligations of the Guarantor
hereunder and otherwise exercise all remedies hereunder and to make all demands
and give all notices and make all requests required or permitted to be made by
the Owner Lessor (in its own name or in the name of the Owner Lessor) under this
Guaranty. If the Guarantor shall receive inconsistent directions from the Owner
Lessor and the Holder Representative, the Guarantor shall follow the directions
of the Holder Representative.

SECTION 5.     SURVIVAL OF GUARANTY

        Notwithstanding anything to the contrary herein, this Guaranty shall
continue to be effective or be reinstated, as the case may be, if at any time
any of the amounts paid to the Beneficiary, in whole or in part, is required to
be repaid upon the insolvency, bankruptcy, dissolution, liquidation, or
reorganization of the Guarantor, Collins Holdings or any other Person, or as a
result of the appointment of a custodian, interviewer, receiver, trustee, or
other officer with similar powers with respect to the Guarantor, Collins
Holdings or any other Person or with respect to any

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substantial part of the property of the Guarantor, Collins Holdings or such
other Person, all as if such payments had not been made.

SECTION 6.     REMEDIES; SUBROGATION

        SECTION 6.1 REMEDIES. In the event the Guarantor shall fail to pay
immediately any amounts due under this Guaranty, or to comply with any other
term of this Guaranty, the Beneficiary shall be entitled to all rights and
remedies to which it may be entitled hereunder or at law, in equity or by
statute.

        SECTION 6.2 SUBROGATION. The Guarantor will not exercise any rights that
it may acquire by way of subrogation under this Guaranty, by any payment made
hereunder or otherwise, until all of the Obligations shall have been paid in
full. If any amount shall be paid to the Guarantor on account of such
subrogation rights at any time when all of the Obligations shall not have been
paid in full, such amount shall be held in trust for the benefit of the
Beneficiary to whom such Obligation is payable and shall forthwith be paid to
such Beneficiary to be credited and applied to such Obligation, whether matured
or unmatured, in accordance with the terms of the Operative Document under which
such Obligation arose. If (i) the Guarantor shall make payment to the
Beneficiary of all or any part of the Obligations and (ii) all the Obligations
shall be paid in full, such Beneficiary will, at the Guarantor's request and
expense, execute and deliver to the Guarantor appropriate documents, without
recourse and with representation or warranty, necessary to evidence the transfer
by subrogation to the Guarantor of an interest in the Obligations resulting from
such payment by the Guarantor.

        SECTION 6.3 SURVIVAL OF REMEDIES AND SUBROGATION RIGHTS. The provisions
of this Section 6 shall survive the termination of this Guaranty and the payment
in full of the Obligations and the termination of the CHE Operative Documents.

SECTION 7.     MISCELLANEOUS

        SECTION 7.1 AMENDMENTS AND WAIVERS. No term, covenant, agreement or
condition of this Guaranty may be terminated, amended or compliance therewith
waived (either generally or in a particular instance, retroactively or
prospectively) except by an instrument or instruments in writing executed by the
Guarantor and consented to by the Beneficiary.

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        SECTION 7.2 NOTICES. Unless otherwise expressly specified or permitted
by the terms hereof, all communications and notices provided for herein shall be
in writing or by a telecommunications device capable of creating a written
record, and any such notice shall become effective (a) upon personal delivery
thereof, including by overnight mail or courier service, (b) in the case of
notice by United States mail, certified or registered, postage prepaid, return
receipt requested, upon receipt thereof, or (c) in the case of notice by such a
telecommunications device, upon transmission thereof, provided such transmission
is promptly confirmed by either of the methods set forth in clauses (a) or (b)
above, in each case addressed to the Guarantor hereto at its address set forth
below or at such other address as such party may from time to time designate by
written notice.

If to the Guarantor:

        Midwest Generation, LLC
        One Financial Place
        440 South LaSalle Street, Suite 3500
        Chicago, IL  60605
        Facsimile No.:  (312) 583-6111
        Attention: Georgia R. Nelson

        SECTION 7.3 SURVIVAL. Except as expressly set forth herein, the
warranties and covenants made by the Guarantor shall not survive the expiration
or termination of this Guaranty.

        SECTION 7.4 ASSIGNMENT AND ASSUMPTION. This Guaranty may not be assigned
by the Guarantor to, or assumed by, any successor to, or assignee of, the
Guarantor without the prior written consent of the Beneficiary.

        SECTION 7.5 GOVERNING LAW. This Guaranty shall be in all respects
governed by and construed in accordance with the laws of the State of New York,
including all matters of construction, validity and performance (without giving
effect to the conflicts of laws provisions, other than New York General
Obligations Law Section 5-1401).

        SECTION 7.6 SEVERABILITY. Any provision of this Guaranty that is
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining

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provisions hereof, and any such prohibition or unenforceability in any
jurisdiction shall not invalidate or render unenforceable such provision in
any other jurisdiction.

        SECTION 7.7 MERGER. This Guaranty constitutes the entire agreement and
supersedes all prior agreements and understandings, both written and oral
between or among the Guarantor, Collins Holdings and the Beneficiary with
respect to the subject matter hereof.

        SECTION 7.8 HEADINGS. The headings of the sections of this Guaranty are
inserted for purposes of convenience only and shall not be construed to affect
the meaning or construction of any of the provisions hereof.

        SECTION 7.9 FURTHER ASSURANCES. The Guarantor will promptly and duly
execute and deliver such further documents to make such further assurances for
and take such further action reasonably requested by the Beneficiary referred to
in Section 4 hereof to whom the Guarantor is obligated, all as may be reasonably
necessary to carry out more effectively the intent and purpose of this Guaranty.

        SECTION 7.10 EFFECTIVENESS OF GUARANTY. This Guaranty shall be effective
on the date of execution and delivery by the Guarantor.

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        IN WITNESS WHEREOF, the Guarantor has caused this Guaranty to be duly
executed and delivered by its officer thereunto duly authorized.

                          MIDWEST GENERATION, LLC
                          as Guarantor

                          By: /s/ Fred W. McCluskey
                             ----------------------
                          Name: Fred W. McCluskey
                          Title: Vice President

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                                                                Exhibit 10.104.1

SCHEDULE IDENTIFYING SUBSTANTIALLY IDENTICAL AGREEMENT(S)  TO EXHIBIT 10.104

Midwest Lessor Lease Guaranty (T2), dated as of December15, 1999, made by
Midwest Generation, LLC.

Midwest Lessor Lease Guaranty (T3), dated as of December15, 1999, made by
Midwest Generation, LLC.

Midwest Lessor Lease Guaranty (T4), dated as of December15, 1999, made by
Midwest Generation, LLC.

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