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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2022-05-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000923571</issuerCik>
        <issuerName>US XPRESS ENTERPRISES INC</issuerName>
        <issuerTradingSymbol>USX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000931421</rptOwnerCik>
            <rptOwnerName>FULLER MAX L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4080 JENKINS ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHATTANOOGA</rptOwnerCity>
            <rptOwnerState>TN</rptOwnerState>
            <rptOwnerZipCode>37421</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle>Executive Chairman</officerTitle>
            <otherText>Member &amp; Co-Trustee</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001743588</rptOwnerCik>
            <rptOwnerName>Fuller Janice</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4080 JENKINS ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHATTANOOGA</rptOwnerCity>
            <rptOwnerState>TN</rptOwnerState>
            <rptOwnerZipCode>37421</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001743589</rptOwnerCik>
            <rptOwnerName>Fuller Family Enterprises, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>4080 JENKINS ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHATTANOOGA</rptOwnerCity>
            <rptOwnerState>TN</rptOwnerState>
            <rptOwnerZipCode>37421</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2022-05-18</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>154803</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.1964</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1577482</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Member</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2022-05-19</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>81000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.0980</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1658482</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Member</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class B Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>333315</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class B Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8261776</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F5"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Member</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class B Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1993269</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F6"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Co-trustee</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>170068</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Price of $3.1964 is a weighted average purchase price for multiple transactions ranging from $3.065 to $3.35, inclusive. The reporting persons undertake to provide, upon request by the SEC staff, the issuer, or a stockholder of the issuer, full information regarding the number of shares purchased at each separate price.</footnote>
        <footnote id="F2">Shares held by Fuller Family Enterprises, LLC, in which Mr. Max Fuller and Ms. Janice Fuller are each members. Mr. Max Fuller and Ms. Janice Fuller each disclaim beneficial ownership of these securities except to the extent of his or her respective pecuniary interest therein, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of all the reported securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F3">Price of $3.0980 is a weighted average purchase price for multiple transactions ranging from $3.06 to $3.18, inclusive. The reporting persons undertake to provide, upon request by the SEC staff, the issuer, or a stockholder of the issuer, full information regarding the number of shares purchased at each separate price.</footnote>
        <footnote id="F4">Shares held by Mr. Max Fuller.</footnote>
        <footnote id="F5">Represents (i) 2,753,926 shares of Class B common stock held by FSBSPE 1, LLC (ii) 2,753,925 shares of Class B common stock held by FSBSPE 2, LLC, and (iii) 2,753,925 shares of Class B common stock held by FSBSPE 3, LLC. FSBSPE 1, LLC FSBSPE 2, LLC, and FSBSPE 3, LLC are wholly owned subsidiaries of Fuller Family Enterprises, LLC, in which Mr. Max Fuller and Ms. Janice Fuller are each members. Mr. Max Fuller and Ms. Janice Fuller each disclaim beneficial ownership of these securities except to the extent of his or her respective pecuniary interest therein, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of all the reported securities for purposes of Section 16 or for any other purpose.</footnote>
        <footnote id="F6">Shares held by the Max L. Fuller 2008 Irrevocable Trust FBO William E. Fuller, over which Ms. Janice Fuller and her son, Mr. Eric Fuller, are the co-trustees and have shared dispositive power and Mr. Eric Fuller has sole voting power. Mr. Max Fuller and Ms. Janice Fuller each disclaim beneficial ownership of these securities except to the extent of his or her respective pecuniary interest therein, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of all the reported securities for purposes of Section 16 or for any other purposes.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Max L. Fuller, by Heidi Hornung-Scherr, attorney-in-fact, pursuant to a POA previously filed with the SEC</signatureName>
        <signatureDate>2022-05-20</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Janice Fuller, by Heidi Hornung-Scherr, attorney-in-fact, pursuant to a POA previously filed with the SEC</signatureName>
        <signatureDate>2022-05-20</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Max L. Fuller, member Fuller Family Enterprises, LLC, by Heidi Hornung-Scherr, attorney-in-fact, pursuant to a POA previously filed with the SEC</signatureName>
        <signatureDate>2022-05-20</signatureDate>
    </ownerSignature>
</ownershipDocument>
