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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-09-09</periodOfReport>

    <issuer>
        <issuerCik>0000095304</issuerCik>
        <issuerName>SUNOCO INC</issuerName>
        <issuerTradingSymbol>SUN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001178443</rptOwnerCik>
            <rptOwnerName>DARNALL ROBERT J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1735 MARKET STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PHILADELPHIA</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19103-7583</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Deferred Share Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-09-09</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18.806</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>71.835</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>1988-08-08</value>
            </exerciseDate>
            <expirationDate>
                <value>1988-08-08</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>18.806</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>595.282</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-09-09</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>18.347</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>71.835</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>1988-08-08</value>
            </exerciseDate>
            <expirationDate>
                <value>1988-08-08</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>18.347</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>857.365</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F5">Total of 6,607.981 Phantom Stock Units beneficially owned following reported transaction.  Reported item reflects the 2-for-1 split of Sunoco, Inc.'s Common Stock effectuated on August 1, 2005.  This stock split resulted in a doubling of the shares of Sunoco Common Stock, and related derivative securities, previously reported as being beneficially owned by the reporting person.  Also, as a result of the split, the trading price of Sunoco Common Stock and the exercise or conversion price of related derivative securities was effectively halved.</footnote>
        <footnote id="F2">Dividend equivalents credited as restricted share units acquired pursuant to the Sunoco, Inc. Directors' Deferred Compensation Plan, in transaction exempt under Rule 16b-3(d).</footnote>
        <footnote id="F3">Total of 6,773.520 Restricted Share Units beneficially owned following reported transaction.  Reported item reflects the 2-for-1 split of Sunoco, Inc.'s Common Stock effectuated on August 1, 2005.  This stock split resulted in a doubling of the shares of Sunoco Common Stock, and related derivative securities, previously reported as being beneficially owned by the reporting person.  Also, as a result of the split, the trading price of Sunoco Common Stock and the exercise or conversion price of related derivative securities was effectively halved.</footnote>
        <footnote id="F4">Crediting of dividend equivalents on voluntary deferred compensation account pursuant to the Sunoco, Inc. Directors Deferred Compensation Plan, in transactions exempt under Rule 16b-3(d).</footnote>
        <footnote id="F1">The conversion rate is 1 for 1.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John J. DiRocco, Jr., Attorney-in-fact for Robert J. Darnall</signatureName>
        <signatureDate>2005-09-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "doc.xml", "description": "PRIMARY DOCUMENT", "secsgml_size_bytes": 7799}]
X0202
4
2005-09-09
0000095304
SUNOCO INC
SUN
0001178443
DARNALL ROBERT J
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2005-09-09
4
A
0
18.806
71.835
A
1988-08-08
1988-08-08
Common Stock
18.806
595.282
D
Phantom Stock Units
2005-09-09
4
A
0
18.347
71.835
A
1988-08-08
1988-08-08
Common Stock
18.347
857.365
D
Total of 6,607.981 Phantom Stock Units beneficially owned following reported transaction.  Reported item reflects the 2-for-1 split of Sunoco, Inc.'s Common Stock effectuated on August 1, 2005.  This stock split resulted in a doubling of the shares of Sunoco Common Stock, and related derivative securities, previously reported as being beneficially owned by the reporting person.  Also, as a result of the split, the trading price of Sunoco Common Stock and the exercise or conversion price of related derivative securities was effectively halved.
Dividend equivalents credited as restricted share units acquired pursuant to the Sunoco, Inc. Directors' Deferred Compensation Plan, in transaction exempt under Rule 16b-3(d).
Total of 6,773.520 Restricted Share Units beneficially owned following reported transaction.  Reported item reflects the 2-for-1 split of Sunoco, Inc.'s Common Stock effectuated on August 1, 2005.  This stock split resulted in a doubling of the shares of Sunoco Common Stock, and related derivative securities, previously reported as being beneficially owned by the reporting person.  Also, as a result of the split, the trading price of Sunoco Common Stock and the exercise or conversion price of related derivative securities was effectively halved.
Crediting of dividend equivalents on voluntary deferred compensation account pursuant to the Sunoco, Inc. Directors Deferred Compensation Plan, in transactions exempt under Rule 16b-3(d).
The conversion rate is 1 for 1.
John J. DiRocco, Jr., Attorney-in-fact for Robert J. Darnall
2005-09-13