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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 GtJavcDimqA3jMftLVsc5DMcikEbcp0/H533/t03b4tuGB4cj+LfBvLftBMfmjpw
 isxTaYAJPQQBmHAiaO168g==

<SEC-DOCUMENT>0001140361-05-001063.txt : 20050208
<SEC-HEADER>0001140361-05-001063.hdr.sgml : 20050208
<ACCEPTANCE-DATETIME>20050208090046
ACCESSION NUMBER:		0001140361-05-001063
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050203
FILED AS OF DATE:		20050208
DATE AS OF CHANGE:		20050208

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SOUTHERN UNION CO
		CENTRAL INDEX KEY:			0000203248
		STANDARD INDUSTRIAL CLASSIFICATION:	NATURAL GAS DISTRIBUTION [4924]
		IRS NUMBER:				750571592
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		ONE PEI CENTER
		CITY:			WILKES-BARRE
		STATE:			PA
		ZIP:			18711
		BUSINESS PHONE:		(570) 820-2400

	MAIL ADDRESS:	
		STREET 1:		ONE PEI CENTER
		CITY:			WILKES-BARRE
		STATE:			PA
		ZIP:			18711

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			LINDEMANN GEORGE L
		CENTRAL INDEX KEY:			0000897631

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-06407
		FILM NUMBER:		05582191

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		5708202400

	MAIL ADDRESS:	
		STREET 1:		767 FIFTH AVENUE
		STREET 2:		50TH FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10153
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-02-03</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000203248</issuerCik>
        <issuerName>SOUTHERN UNION CO</issuerName>
        <issuerTradingSymbol>SUG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000897631</rptOwnerCik>
            <rptOwnerName>LINDEMANN GEORGE L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>767 FIFTH AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10153</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2005-02-03</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>149.5456</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.71</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>66828.91</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Supplemental Plan</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">All shares reported hereon, have been adjusted to reflect the 5% stock dividend distributed to shareholders of record on August 20, 2004.</footnote>
        <footnote id="F2">The Reporting Person also indirectly holds 22,627 shares of common stock through the Issuer's 401(K) Plan, 3,180,136 and 3,133,867 shares of common stock through SUG 1, L.P. and SUG 2 L.P., respectively.</footnote>
        <footnote id="F3">This information concerns shares held under the Issuer?s Supplemental Deferred Compensation Plan.  This report also reflects shares purchased for the plan by the plan trustee, at the sole discretion of the trustee, at such prices as were available in the open market at the time of such purchases.  The purchase price, as reported, is exclusive of an $.08 per share brokerage commission.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Dennis K. Morgan for George L. Lindemann</signatureName>
        <signatureDate>2005-02-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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