<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-04-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001024725</issuerCik>
        <issuerName>TENNECO INC</issuerName>
        <issuerTradingSymbol>TEN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000921669</rptOwnerCik>
            <rptOwnerName>ICAHN CARL C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ICAHN ASSOCIATES HOLDINGS LLC</rptOwnerStreet1>
            <rptOwnerStreet2>16690 COLLINS AVENUE - PENTHOUSE SUITE</rptOwnerStreet2>
            <rptOwnerCity>SUNNY ISLES BEACH</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33160</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001034563</rptOwnerCik>
            <rptOwnerName>ICAHN ENTERPRISES HOLDINGS L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>16690 COLLINS AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>PENTHOUSE SUITE</rptOwnerStreet2>
            <rptOwnerCity>SUNNY ISLES BEACH</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33160</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001257324</rptOwnerCik>
            <rptOwnerName>ICAHN ENTERPRISES G.P. INC.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>16690 COLLINS AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>PENTHOUSE SUITE</rptOwnerStreet2>
            <rptOwnerCity>SUNNY ISLES BEACH</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33160</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001080113</rptOwnerCik>
            <rptOwnerName>BECKTON CORP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>16690 COLLINS AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>PENTHOUSE SUITE</rptOwnerStreet2>
            <rptOwnerCity>SUNNY ISLES BEACH</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33160</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2020-04-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3485215</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F6"/>
                    <footnoteId id="F7"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>9136392</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Please see footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                    <footnoteId id="F7"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Class B Common Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F6"/>
                <footnoteId id="F7"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-04-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>C</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3485215</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F6"/>
                <footnoteId id="F7"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F6"/>
                <footnoteId id="F7"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3485215</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>20308454</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Please see footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                    <footnoteId id="F6"/>
                    <footnoteId id="F7"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Icahn Enterprises Holdings L.P. (&quot;Icahn Enterprises Holdings&quot;) is the direct beneficial owner of (i) 9,136,392 shares of Class A Common Stock and (ii) 17,232,791 shares of Class B Common Stock. Beckton Corp. (&quot;Beckton&quot;) is the sole stockholder of Icahn Enterprises G.P. Inc. (&quot;Icahn Enterprises GP&quot;), which is the general partner of Icahn Enterprises Holdings. Mr. Icahn is the sole stockholder of Beckton.</footnote>
        <footnote id="F2">In addition, Mr. Icahn is the indirect holder of approximately 92.0% of the outstanding depositary units representing limited partnership interests in Icahn Enterprises L.P. (&quot;Icahn Enterprises&quot;). Icahn Enterprises GP is the general partner of Icahn Enterprises, which is the sole limited partner of Icahn Enterprises Holdings.</footnote>
        <footnote id="F3">By virtue of their relationships to Icahn Enterprises Holdings, each of Icahn Enterprises GP, Beckton and Mr. Icahn may be deemed to indirectly beneficially own the shares of Class A Common Stock and Class B Common Stock held directly by Icahn Enterprises Holdings. Each of the foregoing disclaims his or its beneficial ownership of such shares of Class A Common Stock and Class B Common Stock except to the extent of his or its pecuniary interest therein.</footnote>
        <footnote id="F4">American Entertainment Properties Corp. (&quot;AEP&quot;) is the direct beneficial owner of 3,075,663 shares of Class B Common Stock. Icahn Enterprises Holdings is the sole member of Icahn Building LLC (&quot;Building&quot;), which is the sole stockholder of AEP.</footnote>
        <footnote id="F5">By virtue of their relationships to AEP, each of Building, Icahn Enterprises Holdings, Icahn Enterprises GP, Beckton and Mr. Icahn may be deemed to indirectly beneficially own the shares of Class B Common Stock held directly by AEP. Each of the foregoing disclaims his or its beneficial ownership of such shares of Class B Common Stock except to the extent of his or its pecuniary interest therein.</footnote>
        <footnote id="F6">The Class B Common Stock is convertible into an equal number of shares of Class A Common Stock and has no expiration date. Pursuant to the terms of a Shareholders Agreement, dated October 1, 2018, among the issuer, AEP, Icahn Enterprises Holdings and Icahn Enterprises, if the separation of the issuer into two separate businesses and distribution of the equity interests in one such business to the issuer's stockholders (the &quot;Spin-Off&quot;) has not occurred by April 1, 2020, Icahn Enterprises and its affiliates may convert their shares of Class B Common Stock into Class A Common Stock to the extent such conversion would not result in Icahn Enterprises and its affiliates owning, in the aggregate, more than 15% of the Class A Common Stock issued and outstanding immediately following such conversion.</footnote>
        <footnote id="F7">The Spin-Off did not occur by April 1, 2020. Therefore, on April 1, 2020, Icahn Enterprises Holdings converted 3,485,215 shares of Class B Common Stock into 3,485,215 shares of Class A Common Stock.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/S/ Carl C. Icahn</signatureName>
        <signatureDate>2020-04-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/S/ Icahn Enterprises Holdings L.P., by Icahn Enterprises G.P. Inc., its general partner, /S/ SungHwan Cho, Chief Financial Officer</signatureName>
        <signatureDate>2020-04-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/S/ Icahn Enterprises G.P. Inc., /S/ SungHwan Cho, Chief Financial Officer</signatureName>
        <signatureDate>2020-04-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/S/ Beckton Corp., /S/ Edward E. Mattner, Authorized Signatory</signatureName>
        <signatureDate>2020-04-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
