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                                                                EXHIBIT 4(a)(10)

                                                                [CONFORMED COPY]
 
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                                  TENNECO INC.
 
                                      AND
 
                            THE CHASE MANHATTAN BANK
                            (NATIONAL ASSOCIATION),
 
                                                                      AS TRUSTEE
 
                              ------------------
 
                         TWELFTH SUPPLEMENTAL INDENTURE
 
                         DATED AS OF DECEMBER 15, 1995
 
                                       TO
 
                                   INDENTURE
 
                           DATED AS OF MARCH 15, 1988
 
                              ------------------
 
                         PROVIDING FOR THE ISSUANCE OF
                           7 1/4% DEBENTURES DUE 2025
 
 
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<PAGE>
 
  Twelfth Supplemental Indenture dated as of December 15, 1995 between Tenneco
Inc., a corporation duly organized and existing under the laws of the State of
Delaware (hereinafter called the "Company"), and The Chase Manhattan Bank
(National Association), a national banking association existing under the laws
of the United States of America, as trustee (hereinafter called the
"Trustee").
 
  Whereas, the Company has heretofore executed and delivered to the Trustee an
indenture dated as of March 15, 1988 (hereinafter called the "Original
Indenture"), to provide for the issue of an unlimited amount of debentures,
notes and/or other debt obligations of the Company (hereinafter referred to as
the "Securities"), the terms of which are to be determined as set forth in
(S) 2.02 of the Original Indenture; and
 
  Whereas, (S) 12.01 of the Original Indenture provides, among other things,
that the Company and the Trustee may enter into indentures supplemental to the
Original Indenture for, among other things, the purpose of setting forth the
terms of Securities of any series; and
 
  Whereas, the Company desires to create a series of the Securities in an
aggregate principal amount of $300,000,000 to be designated the "7 1/4%
Debentures due 2025" (the "Debentures"), and all action on the part of the
Company necessary to authorize the issuance of the Debentures under the
Original Indenture and this Twelfth Supplemental Indenture has been duly
taken; and
 
  Whereas, all acts and things necessary to make the Debentures, when executed
by the Company and authenticated and delivered by the Trustee as in the
Indenture provided, the valid and binding obligations of the Company, and to
constitute these presents a valid and binding supplemental indenture and
agreement according to its terms, have been done and performed;
 
  Now, therefore, in consideration of the premises and of the mutual covenants
herein contained, and of the acceptance of this trust by the Trustee, and of
the sum of one dollar to the Company duly paid by the Trustee at the execution
and delivery of these presents, and of other valuable consideration the
receipt whereof is hereby acknowledged and in order to authorize the
authentication and delivery of and to set forth the terms of the Debentures,
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                                      2
 
  It is hereby covenanted, declared and agreed by and between the parties
hereto, for the benefit of holders of the Debentures issued under the
Indenture, as follows:
 
                                  ARTICLE 1.
 
               Terms and Issuance of 7 1/4% Debentures Due 2025
 
  (S) 1.01. Issue of Debentures. A series of Securities which shall be
designated the "7 1/4% Debentures due 2025" shall be executed, authenticated
and delivered in accordance with the provisions of, and shall in all respects
be subject to, the terms, conditions and covenants of the Indenture, including
without limitation the terms set forth in this Twelfth Supplemental Indenture
(including the form of Debentures set forth in (S) 1.02 hereof). The aggregate
principal amount of Debentures which may be authenticated and delivered under
the Indenture shall not, except as permitted by the provisions of (S)(S) 2.07,
2.08, 2.10, 2.11 or 3.02 of the Indenture, exceed $300,000,000. The entire
amount of Debentures may forthwith be executed by the Company and delivered to
the Trustee and shall be authenticated by the Trustee and delivered to or upon
the order of the Company pursuant to (S) 2.03 of the Indenture.
 
  (S) 1.02. Forms of Debentures and Authentication Certificate. The forms of
the Debentures and the Trustee's certificate of authentication shall be
substantially as follows:
 
                          [form of face of debenture]
                 [To be inserted on face of Global Debentures]
 
  [Unless and until this Debenture is exchanged in whole or in part for
Debentures in definitive registered form, this Debenture may not be
transferred except as a whole by the Depositary (as defined in the Indenture
(as defined below)) to the nominee of the Depositary or by a nominee of the
Depositary to the Depositary or another nominee of the Depositary or by the
Depositary or any such nominee to a successor Depositary or a nominee of such
successor Depositary.
 
  Unless this Debenture is presented by an authorized representative of The
Depository Trust Company, a New York corporation ("DTC"), to the Company (as
defined below) or its agent for registration of transfer, exchange, or
payment, and any certificate issued is registered in the name of Cede & Co. or
in such other name as is requested by an authorized representative of DTC (and
any payment is made to Cede & Co. or to such other entity as is requested by
an authorized representative of DTC), ANY TRANSFER, PLEDGE, OR OTHER USE
HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the
registered owner hereof, Cede & Co., has an interest herein.]
 
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                                      3
 
                                 TENNECO INC.
 
                           7 1/4% DEBENTURE DUE 2025
 
No.                                                                    $
CUSIP
 
  Tenneco Inc., a corporation organized and existing under the laws of the
State of Delaware (hereinafter called the "Company," which term shall include
any successor corporation as defined in the Indenture hereinafter referred
to), for value received, hereby promises to pay to               or registered 
assigns, the sum of      Dollars on December 15, 2025, in any coin or currency 
of the United States of America which at the time of payment is legal tender for
the payment of public and private debts, and to pay to the registered holder
hereof as hereinafter provided interest thereon at the rate per annum specified
in the title hereof in like coin or currency, from the June 15 or December 15
next preceding the date hereof to which interest has been paid, unless the date
hereof is a June 15 or December 15 to which interest on the Debentures has been
paid, in which case from the date hereof, or unless no interest has been paid on
the Debentures since the original issue date (hereinafter referred to) of this
Debenture, in which case from the original issue date, semi-annually on June 15
and December 15 in each year, until payment of said principal sum has been made
or duly provided for, and to pay interest on any overdue principal and (to the
extent permitted by law) on any overdue installment of interest at the rate of 7
1/4% per annum. Notwithstanding the foregoing, when there is no existing default
in the payment of interest on the Debentures, if the date hereof is after May 31
or November 30 and prior to the following June 15 or December 15, as the case
may be, this Debenture shall bear interest from such June 15 or December 15;
provided, however, that if the Company shall default in the payment of interest
due on such June 15 or December 15, then this Debenture shall bear interest from
the June 15 or December 15 to which interest has been paid or, if no interest
has been paid on the Debentures since the original issue date of this Debenture,
from the original issue date. The interest so payable on any June 15 or December
15 will, subject to certain exceptions provided in the Indenture hereinafter
referred to, be paid to the person in whose name this Debenture is registered at
the close of business on the May 31 or November 30, as the case may be, next
preceding such June 15 or December 15, or if such May 31 or November 30 is not a
business day, the business day next preceding such May 31 or November 30.
Interest on this Debenture shall be computed on the basis of a 360-day year
consisting of twelve 30-day months. Both principal of and interest on this
Debenture are payable at the principal office of the Trustee in
 
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                                      4
 
the Borough of Manhattan, The City of New York, New York; provided, however,
that payment of interest may be made, at the option of the Company, by check
mailed to the address of the person entitled thereto as such address shall
appear on the Debenture register. The original issue date in respect of the
Debentures is December 15, 1995.
 
  ADDITIONAL PROVISIONS OF THIS DEBENTURE ARE CONTAINED ON THE REVERSE HEREOF
AND SUCH PROVISIONS SHALL FOR ALL PURPOSES HAVE THE SAME EFFECT AS THOUGH
FULLY SET FORTH AT THIS PLACE.
 
  This Debenture shall not be entitled to any benefit under the Indenture
hereinafter referred to, or become valid or obligatory for any purpose, until
the Trustee under the Indenture shall have signed the form of certificate of
authentication endorsed hereon.
 
  In Witness Whereof, Tenneco Inc. has caused this Instrument to be signed in
its name by its Chairman of the Board or its President or a Vice President,
and its corporate seal (or a facsimile thereof) to be hereto affixed and
attested by its Secretary or an Assistant Secretary.
 
Dated ..........................
 
                                   Tenneco Inc.
 
                                     By .......................................
                                                                 Vice President
 
Attest:
 
 ................................
                      Secretary.
 
<PAGE>
 
                                      5
 
                        [form of reverse of debenture]
 
                                 TENNECO INC.
 
                           7 1/4% DEBENTURE DUE 2025
 
  This Debenture is one of a duly authorized issue of Debentures of the
Company known as its 7 1/4% Debentures due 2025 (herein called the
"Debentures"), limited to the aggregate principal amount of $300,000,000, all
issued under and equally entitled to the benefits of an Indenture (herein,
together with any amendments and supplements thereto, including without
limitation the form and terms of Securities issued pursuant thereto, called
the "Indenture"), dated as of March 15, 1988, executed by the Company to The
Chase Manhattan Bank (National Association) (herein, together with any
successor thereto, called the "Trustee"), as Trustee, to which Indenture
reference is hereby made for a statement of the rights thereunder of the
Trustee and of the registered holders of the Debentures and of the duties
thereunder of the Trustee and the Company.
 
  The Debentures will not be redeemable prior to maturity.
 
  The Indenture permits the Company to issue unsecured debentures, notes
and/or other evidences of indebtedness in one or more series ("Securities") up
to such principal amount or amounts as may be authorized in accordance with
the terms of the Indenture.
 
  To the extent permitted by, and as provided in, the Indenture, modifications
or alterations of the Indenture and of the rights and obligations of the
Company and of the holders of the Debentures may be made with the consent of
the Company and with the consent of the holders of not less than a majority in
principal amount of the Securities of all series then outstanding under the
Indenture (treated as a single class) which are affected by the modification
or amendment thereto; provided, however, that without the consent of the
holder hereof no such modification or alteration shall be made which will
affect the terms of payment of the principal of or interest on this Debenture.
 
  In case a default, as defined in the Indenture, shall occur, the principal
of all the Debentures at any such time outstanding under the Indenture may be
declared or may become due and payable, upon the conditions and in the manner
and with the effect provided in the Indenture. The Indenture provides that
such declaration may in certain events be waived by the holders of a majority
in principal amount of the Debentures outstanding in the case of
 
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                                      6
 
payment defaults on the Debentures and in certain other events by the holders
of a majority in principal amount of the Securities of all series then
outstanding under the Indenture (treated as a single class) which are affected
thereby.
 
  The Indenture provides that no holder of any Debenture may enforce any
remedy under the Indenture except in the case of refusal or neglect of the
Trustee to act after notice of default and after request by the holders of a
majority in principal amount of the outstanding Debentures in certain events
(and in certain other events by the holders of a majority in principal amount
of the Securities of all series then outstanding under the Indenture, treated
as a single class, which are affected thereby) and the offer to the Trustee of
security and indemnity satisfactory to it; provided, however, that such
provision shall not prevent the holder hereof from enforcing payment of the
principal of or interest on this Debenture.
 
  The transfer of this Debenture is registrable by the registered holder
hereof, in person or by duly authorized attorney, at the agency of the Company
in the Borough of Manhattan, The City of New York, New York, on books of the
Company to be kept for that purpose at said agency, upon surrender and
cancellation of this Debenture and on presentation of a duly executed written
instrument of transfer, and thereupon a new Debenture or Debentures, of the
same aggregate principal amount and in authorized denominations, will be
issued to the transferee or transferees in exchange herefor; and this
Debenture, with or without other Debentures, may in like manner be exchanged
for one or more new Debentures of other authorized denominations but of the
same aggregate principal amount; all subject to the terms and conditions set
forth in the Indenture.
 
  The Company, the Trustee, any paying agent and any Registrar of the
Debentures may deem and treat the person in whose name this Debenture is
registered as the absolute owner hereof for all purposes whatsoever, and
neither the Company nor the Trustee nor any paying agent nor any Registrar of
the Debentures shall be affected by any notice to the contrary.
 
  No recourse shall be had for the payment of the principal of or the interest
on, this Debenture, or for any claim based hereon or on the Indenture, against
any incorporator, or against any stockholder, director or officer, as such,
past, present or future, of the Company, or of any predecessor or successor
corporation, either directly or through the Company or any such predecessor or
successor corporation, whether by virtue of any constitution, statute or rule
of law, or by the enforcement of any assessment or penalty or otherwise, all
such liability, whether at common law, in equity, by any constitution, statute
 
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                                      7
 
or otherwise, of incorporators, stockholders, directors or officers being
released by every owner hereof by the acceptance of this Debenture and as part
of the consideration for the issue hereof, and being likewise released by the
terms of the Indenture; provided, however, that nothing herein or in the
Indenture contained shall be taken to prevent recourse to and the enforcement
of the liability, if any, of any stockholder or subscriber to capital stock of
the Company upon or in respect of shares of capital stock not fully paid up.
 
  All terms used in this Debenture which are defined in the Indenture shall
have the meanings assigned to them in the Indenture.
 
               [form of trustee's certificate of authentication]
 
  This Debenture is one of the 7 1/4% Debentures due 2025 described in the
within-mentioned Indenture.
 
                                   THE CHASE MANHATTAN BANK
                                     (National Association),
                                                                       Trustee,
 
                                       By.....................................
                                                   Authorized Officer.
 
  (S) 1.03. Global Securities.
 
  The Debentures shall be issued in the form of one or more Global Securities
that (i) shall represent and shall be denominated in an amount equal to the
aggregate principal amount of all of the Debentures not yet cancelled, (ii)
shall be registered in the name of the Depositary or the nominee of such
Depositary, (iii) shall be delivered by the Trustee to such Depositary or
pursuant to such Depositary's instruction, and (iv) shall bear a legend
substantially to the following effect: "Unless and until it is exchanged in
whole or in part for Debentures in definitive registered form, this Debenture
may not be transferred except as a whole by the Depositary to the nominee of
the Depositary or by a nominee of the Depositary to the Depositary or another
nominee of the Depositary or by the Depositary or any such nominee to a
successor Depositary or a nominee of such successor Depositary."
 
  Each Depositary designated must, at the time of its designation and at all
times while it serves as Depositary, be a clearing agency registered under the
Securities Exchange Act of 1934 and any other applicable statute or
regulation.
 
<PAGE>
 
                                      8
 
  Notwithstanding the Indenture, any Debentures represented by a Global
Security may not, except as set forth below, be exchanged for a Debenture or
Debentures having authorized denominations and an equal aggregate principal
amount, upon surrender of Debentures to be exchanged at the office of the
Registrar.
 
  Notwithstanding any other provision of this Twelfth Supplemental Indenture,
unless and until it is exchanged in whole or in part for Debentures in
definitive registered form, a Global Security representing all or a part of
the Debentures may not be transferred except as a whole by the Depositary for
such series to a nominee of such Depositary or by a nominee of such Depositary
to such Depositary or another nominee of such Depositary or by such Depositary
or any such nominee to a successor Depositary for such series or a nominee of
such successor Depositary.
 
  If at any time the Depositary for the Debentures represented by one or more
Global Securities notifies the Company that it is unwilling or unable to
continue as Depositary for such Debentures or if at any time the Depositary
for such Debentures shall no longer be eligible under this Twelfth
Supplemental Indenture, the Company shall appoint a successor Depositary with
respect to such Debentures. If a successor Depositary for such Debentures is
not appointed by the Company within 90 days after the Company receives such
notice or becomes aware of such ineligibility, the Company's election that
such Debentures be represented by one or more Global Securities shall no
longer be effective and the Company shall execute, and the Trustee, upon
receipt of instructions from the Company for the authentication and delivery
of definitive Debentures, will authenticate and deliver Debentures in
definitive registered form, in any authorized denominations, in an aggregate
principal amount equal to the principal amount of the Global Security or
Securities representing such Debentures in exchange for such Global Security
or Securities.
 
  The Company may at any time and in its sole discretion determine that the
Debentures issued in the form of one or more Global Securities shall no longer
be represented by a Global Security or Securities. In such event the Company
shall execute, and the Trustee, upon receipt of an Officers' Certificate for
the authentication and delivery of definitive Debentures, shall authenticate
and deliver, Debentures in definitive registered form, in any authorized
denominations, in an aggregate principal amount equal to the principal amount
of the Global Security or Securities representing such Debentures, in exchange
for such Global Security or Securities.
 
<PAGE>
 
                                      9
 
  The Depositary for such Global Security may surrender such Global Security
in exchange in whole or in part for Debentures in definitive registered form
on such terms as are acceptable to the Company and such Depositary. Thereupon,
the Company shall execute, and the Trustee shall authenticate and deliver,
without service charge,
 
    (i) to the Person specified by such Depositary, a new Security or
  Securities of the same series as the Debentures, of any authorized
  denominations as requested by such Person, in an aggregate principal amount
  equal to and in exchange for such Person's beneficial interest in the
  Global Security; and
 
    (ii) to such Depositary a new Global Security in a denomination equal to
  the difference, if any, between the principal amount of the surrendered
  Global Security and the aggregate principal amount of the Debentures
  authenticated and delivered pursuant to clause (i) above.
 
  Upon the exchange of a Global Security for Debentures in definitive
registered form in authorized denominations, such Global Security shall be
cancelled by the Trustee or an agent of the Company or the Trustee. Debentures
in definitive registered form issued in exchange for a Global Security
pursuant to this Section 1.03 shall be registered in such names and in such
authorized denominations as the Depositary for such Global Security, pursuant
to instructions from its direct or indirect participants or otherwise, shall
instruct the Trustee or an agent of the Company or the Trustee. The Trustee or
such agent shall deliver at its office such Debentures to or as directed by
the Persons in whose names such Securities are so registered.
 
  "Depositary" means, with respect to the Debentures, The Depository Trust
Company until a successor Depositary shall have become such pursuant to the
applicable provisions of this Twelfth Supplemental Indenture, and thereafter
"Depositary" shall mean or include each Person who is then a Depositary
hereunder, and, if at any time there is more than one such Person,
"Depositary" as used with respect to the Debentures shall mean the Depositary
with respect to the Global Securities.
 
  "Global Security" means a Security evidencing all or a part of the
Debentures issued to the Depositary and bearing the legend prescribed in this
Twelfth Supplemental Indenture.
 
<PAGE>
 
                                      10
 
                                  ARTICLE 2.
 
                                 Miscellaneous
 
  (S) 2.01. Execution as Supplemental Indenture. This Twelfth Supplemental
Indenture is executed and shall be construed as an indenture supplemental to
the Original Indenture and, as provided in the Original Indenture, this
Twelfth Supplemental Indenture forms a part thereof. Except as herein
expressly otherwise defined, the use of the terms and expressions herein is in
accordance with the definitions, uses and constructions contained in the
Original Indenture.
 
  (S) 2.02. Responsibility for Recitals, Etc. The recitals herein and in the
Debentures (except in the Trustee's certificate of authentication) shall be
taken as the statements of the Company, and the Trustee assumes no
responsibility for the correctness thereof. The Trustee makes no
representations as to the validity or sufficiency of this Twelfth Supplemental
Indenture or of the Debentures. The Trustee shall not be accountable for the
use or application by the Company of the Debentures or of the proceeds
thereof.
 
  (S) 2.03. Provisions Binding on Company's Successors. All the covenants,
stipulations, promises and agreements in this Twelfth Supplemental Indenture
contained by the Company shall bind its successors and assigns whether so
expressed or not.
 
  (S) 2.04. New York Contract. This Twelfth Supplemental Indenture and each
Debenture shall be deemed to be a contract made under the laws of the State of
New York, and for all purposes shall be construed in accordance with the laws
of said State without regard to principles of conflicts of laws.
 
  (S) 2.05. Execution and Counterparts. This Twelfth 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.
 
<PAGE>
 
                                      11
 
  In Witness Whereof, said Tenneco Inc. has caused this Twelfth Supplemental
Indenture to be executed in its corporate name by its Chairman of the Board or
its President or one of its Vice Presidents, and said The Chase Manhattan Bank
(National Association) has caused this Indenture to be executed in its
corporate name by one of its Vice Presidents as of December 15, 1995.
 
                                   Tenneco Inc.
 
                                                 Robert T. Blakely
                                   By _________________________________________
                                                 Robert T. Blakely
                                               Senior Vice President
 
                                   The Chase Manhattan Bank
                                     (National Association)
 
                                                   Valerie Dunbar
                                   By _________________________________________
                                                   Valerie Dunbar
                                                   Vice President