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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2008-09-04</periodOfReport>

    <dateOfOriginalSubmission>2008-09-05</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000788965</issuerCik>
        <issuerName>HALLADOR PETROLEUM CO</issuerName>
        <issuerTradingSymbol>hpco</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001425718</rptOwnerCik>
            <rptOwnerName>Martin Lawrence D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>215 TIMBERLINE DR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>GEORGETOWN</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>61846</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>CFO - Sunrise Coal, LLC</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>common stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2008-09-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>4.4</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13000</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Number of shares actually purchased on September 4, 2008 were 2,000, not the 2,200 shares originally reported.</footnote>
        <footnote id="F2">Shares beneficially owned as of September 4, 2008 are 13,000, not the 13,200 originally reported.</footnote>
    </footnotes>

    <remarks>This amended Form 4/A is being filed to correct the number of shares reported as purchased on September 4, 2008.  The original Form 4 reported that 2,200 shares were purchased and the correct number of shares purchased on September 4, 2008 were 2,000.  This changes Mr. Martin's total ownership of common stock from 13,200 shares to 13,000 shares.</remarks>

    <ownerSignature>
        <signatureName>Victor P. Stabio - attorney-in-fact for Lawrence Martin</signatureName>
        <signatureDate>2008-09-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
