<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>3</documentType>
<periodOfReport>2000-08-07</periodOfReport>
    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000893813</issuerCik>
        <issuerName>PENN OCTANE CORP</issuerName>
        <issuerTradingSymbol>POCC</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001207642</rptOwnerCik>
            <rptOwnerName>BENENSON HARVEY L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>14 EAST 60TH STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 1002</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>0</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle></officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<derivativeTable>
<derivativeHolding>
<securityTitle>
<value>Warrants to purchase POCC Common Stock</value>
</securityTitle>
<conversionOrExercisePrice>
<value>6.69</value>
</conversionOrExercisePrice>
<exerciseDate>
<value>2000-08-07</value>
</exerciseDate>
<expirationDate>
<value>2005-08-06</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Warrants</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>30000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding>
<securityTitle>
<value>Warrants to purchase POCC Common Stock</value>
</securityTitle>
<conversionOrExercisePrice>
<value>4.04</value>
</conversionOrExercisePrice>
<exerciseDate>
<value>2001-08-07</value>
</exerciseDate>
<expirationDate>
<value>2006-08-07</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Warrants</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>10000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding>
<securityTitle>
<value>Warrants to purchase POCC Common Stock</value>
</securityTitle>
<conversionOrExercisePrice>
<value>3.10</value>
</conversionOrExercisePrice>
<exerciseDate>
<value>2002-08-07</value>
</exerciseDate>
<expirationDate>
<value>2007-08-06</value>
</expirationDate>
<underlyingSecurity>
<underlyingSecurityTitle>
<value>Warrnants</value>
</underlyingSecurityTitle>
<underlyingSecurityShares>
<value>10000</value>
</underlyingSecurityShares>
</underlyingSecurity>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value>
</directOrIndirectOwnership>
<natureOfOwnership>
<value></value>
</natureOfOwnership>
</ownershipNature>
</derivativeHolding>
</derivativeTable>
<remarks></remarks>
<ownerSignature>
<signatureName>Harvey L. Benenson</signatureName>
<signatureDate>2003-08-07</signatureDate>
</ownerSignature>
</ownershipDocument>

