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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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<SEC-DOCUMENT>0001140361-06-016045.txt : 20061113
<SEC-HEADER>0001140361-06-016045.hdr.sgml : 20061113
<ACCEPTANCE-DATETIME>20061113151645
ACCESSION NUMBER:		0001140361-06-016045
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20061108
FILED AS OF DATE:		20061113
DATE AS OF CHANGE:		20061113

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:		5444 WESTHEIMER RD
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77056-5306
		BUSINESS PHONE:		(713) 989-2000

	MAIL ADDRESS:	
		STREET 1:		5444 WESTHEIMER RD
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77056-5306

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BRODSKY DAVID L
		CENTRAL INDEX KEY:			0001183999

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-06407
		FILM NUMBER:		061208511

	BUSINESS ADDRESS:	
		STREET 1:		259 CLARK AVE
		CITY:			PALM BEACH
		STATE:			FL
		ZIP:			33480
		BUSINESS PHONE:		5708202400

	MAIL ADDRESS:	
		STREET 1:		C/O SOUTHERN UNION CO
		STREET 2:		ONE PEI CENTER
		CITY:			WILKES BARRE
		STATE:			PA
		ZIP:			18711-0601
</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>2006-11-08</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001183999</rptOwnerCik>
            <rptOwnerName>BRODSKY DAVID L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>259 CLARKE AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PALM BEACH</rptOwnerCity>
            <rptOwnerState>FL</rptOwnerState>
            <rptOwnerZipCode>33480</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>2006-11-08</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>27.565</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>47787</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12215.079</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Director's Deferred Compensation Plan</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4513.95</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Trustee for David L. Brodsky Retirement Plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The grant of shares was adopted by the Compensation Committee of the Board of Directors on May 1, 2006, to be effective on the later of the approval of certain amendments to the Southern Union Company Second Amended and Restated 2003 Stock and Incentive Plan by the Massachusetts Department of Telecommunications and Energy (MDTE) and the filing of a Form S-8 with the Securities and Exchange Commission (SEC).  MDTE approval was received on October 13, 2006 and the Form S-8 was filed with the SEC on November 8, 2006.  As such, this grant of shares became effective on November 8.  The restrictions on the shares associated with this grant expire on January 2, 2007.</footnote>
        <footnote id="F2">This amount includes 4,200 restricted shares which vested on January 2, 2006.</footnote>
        <footnote id="F3">This information concerns shares held under the Issuer's Director's Deferred Compensation Plan. This report reflects shares purchased for the plan by the plan trustee, at such prices as were available in the open market at the time of such purchases.  Information reported herein is based on a plan statement for the period ended December 31, 2005.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Robert M. Kerrigan, III for David L. Brodsky</signatureName>
        <signatureDate>2006-11-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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