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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-03-30</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000316300</issuerCik>
        <issuerName>EXCO RESOURCES INC</issuerName>
        <issuerTradingSymbol>XCO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001394808</rptOwnerCik>
            <rptOwnerName>Serota Jeffrey</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ARES MANAGEMENT, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>1999 AVENUE OF THE STARS, SUITE 1900</rptOwnerStreet2>
            <rptOwnerCity>LOS ANGELES</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>90067</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Director Stock Option</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-03-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>See footnote</value>
                    <footnoteId id="F1"/>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <footnoteId id="F1"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">These stock options were issued pursuant to the Issuer's 2005 Long Term Incentive Plan and represent the right to purchase 50,000 shares of the Issuer's common stock, par value $0.001 per share.  These stock options are held by the Reporting Person for the benefit of Ares Management LLC (&quot;Ares&quot;) and certain funds managed by or affiliated with Ares (together with Ares, the &quot;Ares Entities&quot;).  Pursuant to the policies of the Ares Entities, the Reporting Person must hold these stock options as a nominee for the sole benefit of the Ares Entities and is assigning all economic, pecuniary and voting rights to Ares.</footnote>
        <footnote id="F2">The Reporting Person is associated with Ares and certain of the other Ares Entities.  However, the Reporting Person disclaims beneficial ownership of these securities and the filing of this Form 4 shall not be deemed an admission that the Reporting Person is the beneficial owner of, or has any interest in, any such securities not directly owned by the Reporting Person for purposes of Section 16 of the Securities Exchange Act of 1934, as amended (the &quot;Exchange Act&quot;), or for any other purpose.</footnote>
        <footnote id="F3">Amounts reported in this Form 4 do not include any securities of the Issuer held by the Ares Entities.  The Reporting Person is associated with Ares and certain of the other Ares Entities.  However, the Reporting Person disclaims beneficial ownership of all securities directly and indirectly held by the Ares Entities. The amounts reported herein shall not be deemed an admission that the Reporting Person is the beneficial owner of, or has any interest in, any such securities not directly owned by the Reporting Person for purposes of Section 16 of the Exchange Act or for any other purpose.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Jeffrey Serota</signatureName>
        <signatureDate>2007-04-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
