Document:

<PAGE>

                                                                  EXHIBIT 4(12)

                          FIRST SUPPLEMENTAL INDENTURE

     THIS FIRST SUPPLEMENTAL INDENTURE is made and entered into as of September
30, 2000 by and among MGM MIRAGE, a Delaware corporation ("MGM MIRAGE"), as
issuer, BELLAGIO MERGER SUB LLC, a Nevada limited liability company (the
"Successor Company"), as subsidiary guarantor and successor by merger to
BELLAGIO, a Nevada corporation (the "Merging Entity"), and The Bank of New York,
as trustee ("the "Trustee") under the Indenture (as defined below). Capitalized
terms not defined herein shall have the same meaning as those ascribed to them
in the Indenture (as defined below).

                                    RECITALS

     WHEREAS, MGM MIRAGE, certain of the subsidiaries of MGM MIRAGE, including
the Merging Entity, as subsidiary guarantors, and the Trustee entered into that
certain Indenture, dated as of May 31, 2000 (as amended and/or supplemented, the
"Indenture");

     WHEREAS, pursuant to that certain Articles of Merger, dated September 28,
2000, by and between the Successor Company and the Merging Entity, the Merging
Entity is being merged with and into the Successor Company on September 30, 2000
(the "Merger"), and immediately following the Merger, MGM MIRAGE will be the
sole member of the Successor Company;

     WHEREAS, the Successor Company, as the surviving entity in the Merger, has
taken all necessary limited liability company action to duly authorize the
execution and delivery of this Supplemental Indenture; and

     WHEREAS, the Successor Company is delivering to the Trustee, concurrently
herewith, the documents required by the Indenture in connection with the Merger
and this Supplemental Indenture;

     NOW, THEREFORE, in consideration of good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties agree, for
the benefit of each other and the holders of the Notes, as follows:

                                    ARTICLE I
                            ASSUMPTION OF OBLIGATIONS

     SECTION 1.01 The Successor Company hereby expressly assumes all of the
obligations of the Merging Entity under the Guarantee and the Indenture upon the
effectiveness of the Merger.

                                   ARTICLE II
                             CONCERNING THE TRUSTEE

     SECTION 2.01 The Trustee hereby accepts the trusts hereby declared and
provided and agrees to perform the same upon the terms and conditions set forth
in the Indenture and in this Supplemental

<PAGE>

Indenture, including the terms and provisions defining and limiting the
liabilities in the performance of the trust created by the Indenture, as
supplemented by this Supplemental Indenture.

     SECTION 2.02 The Trustee shall not be responsible in any manner whatsoever
for or in respect of the validity or sufficiency of this Supplemental Indenture
or the due execution hereof by the Successor Company.

                                   ARTICLE III
                                  MISCELLANEOUS

     SECTION 3.01 Upon the execution and delivery of this Supplemental Indenture
by the Successor Company and the Trustee, the Indenture shall be supplemented in
accordance herewith, and this Supplemental Indenture shall form a part of the
Indenture for all purposes, and every holder of Notes heretofore or hereafter
authenticated and delivered under the Indenture shall be bound thereby.

     SECTION 3.02 The Trustee may place an appropriate notation about the
Supplemental Indenture on any Note authenticated after the execution and
delivery of this Supplemental Indenture. MGM MIRAGE may, in its sole discretion,
issue in exchange for all outstanding Notes, and the Trustee shall then
authenticate, new Notes that reflect the Supplemental Indenture.

     SECTION 3.03 Except as modified herein, the Indenture is in all respects
confirmed and preserved, and all provisions of the Indenture shall remain in
full force and effect.

     SECTION 3.04 This Supplemental Indenture may be executed in any number of
counterparts, and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same instrument.

     SECTION 3.05 This Supplemental Indenture shall be governed by and construed
in accordance with the internal laws of the State of Nevada, without regard to
the conflicts of laws rules thereof.

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be executed as of the day and year first above written.

                               MGM MIRAGE,
                               AS ISSUER

                               By: SCOTT LANGSNER
                                   -----------------------------------------
                                   Name: Scott Langsner
                                   Title:  Secretary/Treasurer

                               BELLAGIO MERGER  SUB  LLC,
                               AS SUBSIDIARY GUARANTOR

                               By: MGM MIRAGE

                               By: SCOTT LANGSNER
                                   -----------------------------------------
                                   Name:    Scott Langsner
                                   Title:  Secretary/Treasurer

                               THE BANK OF NEW YORK,
                               AS TRUSTEE

                               By: STACEY POINDEXTER
                                   -----------------------------------------
                                   Name:  Stacey Poindexter
                                   Title: Assistant Treasurer<PAGE>

                                                                 EXHIBIT 4(13)

                          SECOND SUPPLEMENTAL INDENTURE

                          Dated as of October 10, 2000

                                     Between

                          MIRAGE RESORTS, INCORPORATED,

                                    AS ISSUER

                                       and

                         FIRSTAR BANK OF MINNESOTA, N.A.

                                   AS TRUSTEE

                    To Indenture Dated as of October 15, 1996

                     7.25% Senior Notes Due October 15, 2006

<PAGE>

     SECOND SUPPLEMENTAL INDENTURE, dated as of October 10, 2000 (the
"Supplemental Indenture"), between Mirage Resorts, Incorporated, a Nevada
corporation (the "Company"), and Firstar Bank of Minnesota, N.A. (the
"Trustee").

     WHEREAS, the Company has executed and delivered the Indenture dated as of
October 15, 1996, as supplemented by a Supplemental Indenture dated as of
October 15, 1996 (as so supplemented, the "Indenture"), to the Trustee to
provide for the issuance of $250,000,000 Principal Amount of the Company's 7.25%
Senior Notes Due October 15, 2006;

     WHEREAS, the Holders of a majority in principal amount of such Notes have
approved an amendment proposed by the Company to Section 4.02 of the Indenture,
and the Company desires to supplement and amend the Indenture accordingly as
contemplated by Section 9.02 thereof; and

     WHEREAS, all things necessary to make this Supplemental Indenture a valid
agreement of the Company and the Trustee in accordance with its terms, and a
valid amendment and supplement to the Indenture, have been done.

     NOW, THEREFORE, for and in consideration of the premises and mutual
covenants herein contained, the Company and the Trustee agree as follows:

                                   ARTICLE ONE
             DEFINITIONS AND OTHER PROVISIONS OF GENERAL APPLICATION

     Unless the context otherwise requires:

     (a)  capitalized terms used herein that are not otherwise defined herein
shall have the meaning assigned to such terms in the Indenture;

     (b)  the singular includes the plural and vice versa; and

     (c)  headings are for convenience of reference only and do not affect
interpretation.

                                   ARTICLE TWO
                           AMENDMENT TO THE INDENTURE

     The Indenture is hereby amended by deleting the second paragraph of Section
4.02 in its entirety and replacing it with the following:

     "If the Company is not subject to, or for any reason is not complying with,
     the requirements of Section 13 or 15(d) of the Exchange Act, the Company
     shall make available to all of the Holders all quarterly and annual reports
     which the Company would have been required to file with the SEC if it were
     subject to the requirements of Section 13 or 15(d) of the Exchange Act,
     including a "Management's Discussion and Analysis of Financial Condition
     and Results of Operations," and with respect to

<PAGE>

     annual financial statements only, a report thereon by the Company's
     independent accountants.  Notwithstanding the immediately preceding
     sentence, if (i) the Company is a subsidiary of a corporation or other
     person ("Parent") which is subject to and is complying with the
     requirements of Section 13 or 15(d) of the Exchange Act, and (ii) Parent
     has guaranteed the payment of the Principal of and interest on the
     Securities in accordance with their terms, then in lieu of complying with
     the foregoing the Company shall make available to all of the Holders, upon
     written request, copies of the annual reports and of the information,
     documents and other reports (or copies of such portions of any of the
     foregoing as the SEC may by rules and regulations prescribe) which Parent
     is required to file with the SEC pursuant to Section 13 or 15(d) of the
     Exchange Act."

                                  ARTICLE THREE
                                  MISCELLANEOUS

     3.1. NOTIFICATION TO HOLDERS.

     The Company shall notify the Holders in accordance with Section 9.02 of the
Indenture of the execution of this Supplemental Indenture.

     3.2. RATIFICATION OF INDENTURE.

     The Indenture, as supplemented by this Supplemental Indenture, is in all
respects ratified and confirmed, and this Supplemental Indenture shall be deemed
part of the Indenture in the manner and to the extent herein and therein
provided.

     3.3. GOVERNING LAW.

     This Supplemental Indenture shall be deemed to be a contract made under the
internal laws of the State of Nevada, and for all purposes shall be construed in
accordance with the laws of said State.

     3.4. SEVERABILITY.

     In case any one or more of the provisions contained in this Supplemental
Indenture shall for any reason be held to be invalid, illegal or unenforceable
in any respect, such invalidity, illegality or unenforceability shall not affect
any other provision of this Supplemental Indenture, but this Supplemental
Indenture shall be construed as if such invalid, illegal or unenforceable
provision had never been contained herein.

     3.5. COUNTERPARTS.

     This Supplemental Indenture may be executed in any number of counterparts,
each of which shall be an original; but such counterparts shall together
constitute but one and the same instrument.

                                       2
<PAGE>

     3.6. EFFECTIVENESS.

     This Supplemental Indenture shall be effective and binding when executed by
the Company and the Trustee.

     3.7. TRUSTEE NOT RESPONSIBLE FOR RECITALS.

     The recitals herein contained are made by the Company and not by the
Trustee, and the Trustee assumes no responsibility for the correctness thereof.
The Trustee makes no representation as to the validity or sufficiency of this
Supplemental Indenture.

     3.8. PERFORMANCE BY TRUSTEE.

     The Trustee, for itself and its successors, accepts the trust of the
Indenture as amended by this Supplemental Indenture and agrees to perform the
same, but only upon the terms and conditions set forth in the Indenture,
including the terms and provisions defining and limiting the liability and
responsibility of the Trustee.

     IN WITNESS WHEREOF, the Company and the Trustee have caused this Second
Supplemental Indenture to be duly executed as of the day and year first above
written.

                                       MIRAGE RESORTS, INCORPORATED

                                       By:   ROBERT H. BALDWIN
                                          ------------------------------------
                                          Name:   Robert H. Baldwin
                                          Title:  President and Chief
                                                    Executive Officer

                                       By:   SCOTT LANGSNER
                                          ------------------------------------
                                          Name:   Scott Langsner
                                          Title:  Secretary and Treasurer

                                       FIRSTAR BANK OF MINNESOTA, N.A.
                                         as Trustee

                                       By:   FRANK P. LESLIE III
                                          ------------------------------------
                                          Name:   Frank P. Leslie III
                                          Title:  Vice President

                                        3

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00022-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00022-of-00352.parquet"}]]