﻿<?xml version="1.0" encoding="utf-8"?>
<InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Version>2.2.0.7</Version>
  <hasSegments>false</hasSegments>
  <ReportName>Asset Retirement Obligations</ReportName>
  <ReportLongName>006060 - Disclosure - Asset Retirement Obligations</ReportLongName>
  <DisplayLabelColumn>true</DisplayLabelColumn>
  <ShowElementNames>false</ShowElementNames>
  <RoundingOption />
  <HasEmbeddedReports>false</HasEmbeddedReports>
  <Columns>
    <Column>
      <LabelColumn>false</LabelColumn>
      <Id>1</Id>
      <Labels>
        <Label Id="1" Label="9 Months Ended" />
        <Label Id="2" Label="Sep. 30, 2010" />
      </Labels>
      <CurrencyCode>USD</CurrencyCode>
      <FootnoteIndexer />
      <hasSegments>false</hasSegments>
      <hasScenarios>false</hasScenarios>
      <Segments />
      <Scenarios />
      <Units>
        <Unit>
          <UnitID>u000</UnitID>
          <UnitType>Standard</UnitType>
          <StandardMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema>
            <MeasureValue>USD</MeasureValue>
            <MeasureNamespace>iso4217</MeasureNamespace>
          </StandardMeasure>
          <Scale>0</Scale>
        </Unit>
        <Unit>
          <UnitID>u001</UnitID>
          <UnitType>Standard</UnitType>
          <StandardMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema>
            <MeasureValue>pure</MeasureValue>
            <MeasureNamespace>xbrli</MeasureNamespace>
          </StandardMeasure>
          <Scale>0</Scale>
        </Unit>
        <Unit>
          <UnitID>u002</UnitID>
          <UnitType>Standard</UnitType>
          <StandardMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema>
            <MeasureValue>shares</MeasureValue>
            <MeasureNamespace>xbrli</MeasureNamespace>
          </StandardMeasure>
          <Scale>0</Scale>
        </Unit>
        <Unit>
          <UnitID>u003</UnitID>
          <UnitType>Divide</UnitType>
          <NumeratorMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema>
            <MeasureValue>USD</MeasureValue>
            <MeasureNamespace>iso4217</MeasureNamespace>
          </NumeratorMeasure>
          <DenominatorMeasure>
            <MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema>
            <MeasureValue>shares</MeasureValue>
            <MeasureNamespace>xbrli</MeasureNamespace>
          </DenominatorMeasure>
          <Scale>0</Scale>
        </Unit>
      </Units>
      <CurrencySymbol>$</CurrencySymbol>
    </Column>
  </Columns>
  <Rows>
    <Row>
      <Id>2</Id>
      <Label>Notes To Financial Statements [Abstract]</Label>
      <Level>0</Level>
      <ElementName>str_NotesToFinancialStatementsAbstract</ElementName>
      <ElementPrefix>str</ElementPrefix>
      <IsBaseElement>false</IsBaseElement>
      <BalanceType>na</BalanceType>
      <PeriodType>duration</PeriodType>
      <ShortDefinition>No definition available.</ShortDefinition>
      <IsReportTitle>false</IsReportTitle>
      <IsSegmentTitle>false</IsSegmentTitle>
      <IsSubReportEnd>false</IsSubReportEnd>
      <IsCalendarTitle>false</IsCalendarTitle>
      <IsTuple>false</IsTuple>
      <IsAbstractGroupTitle>true</IsAbstractGroupTitle>
      <IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow>
      <IsEquityAdjustmentRow>false</IsEquityAdjustmentRow>
      <IsBeginningBalance>false</IsBeginningBalance>
      <IsEndingBalance>false</IsEndingBalance>
      <IsReverseSign>false</IsReverseSign>
      <PreferredLabelRole />
      <IsEPS>false</IsEPS>
      <FootnoteIndexer />
      <Cells>
        <Cell>
          <Id>1</Id>
          <ShowCurrencySymbol>false</ShowCurrencySymbol>
          <IsNumeric>false</IsNumeric>
          <IsRatio>false</IsRatio>
          <DisplayZeroAsNone>false</DisplayZeroAsNone>
          <NumericAmount>0</NumericAmount>
          <RoundedNumericAmount>0</RoundedNumericAmount>
          <NonNumbericText />
          <NonNumericTextHeader />
          <FootnoteIndexer />
          <hasSegments>false</hasSegments>
          <hasScenarios>false</hasScenarios>
          <DisplayDateInUSFormat>false</DisplayDateInUSFormat>
        </Cell>
      </Cells>
      <OriginalInstanceReportColumns />
      <ElementDataType>xbrli:stringItemType</ElementDataType>
      <SimpleDataType>string</SimpleDataType>
      <ElementDefenition>No definition available.</ElementDefenition>
      <IsTotalLabel>false</IsTotalLabel>
    </Row>
    <Row>
      <Id>3</Id>
      <Label>Asset Retirement Obligations</Label>
      <Level>1</Level>
      <ElementName>us-gaap_AssetRetirementObligationDisclosureTextBlock</ElementName>
      <ElementPrefix>us-gaap</ElementPrefix>
      <IsBaseElement>true</IsBaseElement>
      <BalanceType>na</BalanceType>
      <PeriodType>duration</PeriodType>
      <ShortDefinition>No definition available.</ShortDefinition>
      <IsReportTitle>false</IsReportTitle>
      <IsSegmentTitle>false</IsSegmentTitle>
      <IsSubReportEnd>false</IsSubReportEnd>
      <IsCalendarTitle>false</IsCalendarTitle>
      <IsTuple>false</IsTuple>
      <IsAbstractGroupTitle>false</IsAbstractGroupTitle>
      <IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow>
      <IsEquityAdjustmentRow>false</IsEquityAdjustmentRow>
      <IsBeginningBalance>false</IsBeginningBalance>
      <IsEndingBalance>false</IsEndingBalance>
      <IsReverseSign>false</IsReverseSign>
      <PreferredLabelRole />
      <IsEPS>false</IsEPS>
      <FootnoteIndexer />
      <Cells>
        <Cell>
          <Id>1</Id>
          <ShowCurrencySymbol>false</ShowCurrencySymbol>
          <IsNumeric>false</IsNumeric>
          <IsRatio>false</IsRatio>
          <DisplayZeroAsNone>false</DisplayZeroAsNone>
          <NumericAmount>0</NumericAmount>
          <RoundedNumericAmount>0</RoundedNumericAmount>
          <NonNumbericText>&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="justify"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;Note 6 - Asset Retirement Obligations&lt;/font&gt;&lt;/div&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block"&gt;&lt;br /&gt;&lt;/div&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="left"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"&gt;Questar records asset retirement obligations (ARO) when there are legal obligations associated with the retirement of tangible long-lived assets. The fair values of retirement costs are estimated based on abandonment costs of similar properties available to field operations and depreciated over the life of the related assets. Revisions to ARO estimates result from changes in expected cash flows or material changes in estimated retirement costs. The ARO liability is adjusted to present value each period through an accretion calculation using a credit-adjusted risk-free interest rate. Income or expense resulting from the settlement of ARO liabilities is included in net gain or (loss) from asset sales on the Consolidated Statements of Income. Changes in ARO were as follows:&lt;/font&gt;&lt;/div&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block"&gt;&lt;br /&gt;&lt;/div&gt;&lt;div&gt;&lt;table style="FONT-FAMILY: times new roman; FONT-SIZE: 10pt" cellspacing="0" cellpadding="0" width="100%"&gt;&lt;tr&gt;&lt;td valign="bottom"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160; &lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom" colspan="2"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="center"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;2010&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom" colspan="2"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="center"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;2009&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;tr&gt;&lt;td style="BORDER-BOTTOM: black 2px solid" valign="bottom"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160; &lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid" valign="bottom"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid" valign="bottom" colspan="2"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="center"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;(recast)&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid; TEXT-ALIGN: left" valign="bottom" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid" valign="bottom"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid" valign="bottom" colspan="2"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="center"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;(recast)&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid; TEXT-ALIGN: left" valign="bottom" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;tr&gt;&lt;td valign="bottom"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160; &lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom" colspan="6"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="center"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;(in millions)&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="#cceeff"&gt;&lt;td valign="bottom" width="76%" align="left"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 9pt; MARGIN-RIGHT: 0pt" align="left"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;ARO liability at December 31&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;$&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;65.0&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;$&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;58.9&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="white"&gt;&lt;td valign="bottom" width="76%" align="left"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 9pt; MARGIN-RIGHT: 0pt" align="left"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;Accretion&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;2.1&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;2.5&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="#cceeff"&gt;&lt;td valign="bottom" width="76%" align="left"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 9pt; MARGIN-RIGHT: 0pt" align="left"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;Liabilities incurred&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;0.7&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;0.4&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="white"&gt;&lt;td valign="bottom" width="76%" align="left"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 9pt; MARGIN-RIGHT: 0pt" align="left"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;Revisions&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;(8.2&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;)&lt;/font&gt;&lt;/td&gt;&lt;td valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;2.4&lt;/font&gt;&lt;/td&gt;&lt;td style="TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="#cceeff"&gt;&lt;td style="BORDER-BOTTOM: black 2px solid" valign="bottom" width="76%" align="left"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 9pt; MARGIN-RIGHT: 0pt" align="left"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;Liabilities settled&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid" valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid; TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid; TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;(0.2&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid; TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;)&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid" valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid; TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid; TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;(0.3&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 2px solid; TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;)&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;tr bgcolor="white"&gt;&lt;td style="BORDER-BOTTOM: black 4px double" valign="bottom" width="76%" align="left"&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 9pt; MARGIN-RIGHT: 0pt" align="left"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;ARO liability at September 30&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 4px double" valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 4px double; TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;$&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 4px double; TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;59.4&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 4px double; TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 4px double" valign="bottom" width="1%" align="right"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 4px double; TEXT-ALIGN: left" valign="bottom" width="1%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;$&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 4px double; TEXT-ALIGN: right" valign="bottom" width="9%"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;63.9&lt;/font&gt;&lt;/td&gt;&lt;td style="BORDER-BOTTOM: black 4px double; TEXT-ALIGN: left" valign="bottom" width="1%" nowrap="nowrap"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: times new roman; FONT-SIZE: 10pt"&gt;&amp;#160;&lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt;&lt;/div&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block"&gt;&lt;br /&gt;&lt;/div&gt;&lt;div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="left"&gt;&lt;font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt"&gt;Wexpro collects from Questar Gas and deposits in trust certain funds related to estimated ARO costs. The funds are recorded in other noncurrent assets on the Condensed Consolidated Balance Sheets and used to satisfy retirement obligations as the properties are abandoned. The accounting treatment of reclamation activities associated with ARO for properties administered under the longstanding Wexpro Agreement is defined in a guideline letter between Wexpro and the Utah Division of Public Utilities and the staff of the Public Service Commission of Wyoming (PSCW).&lt;/font&gt;&lt;/div&gt;</NonNumbericText>
          <NonNumericTextHeader>Note 6 - Asset Retirement ObligationsQuestar records asset retirement obligations (ARO) when there are legal obligations associated with the retirement of</NonNumericTextHeader>
          <FootnoteIndexer />
          <hasSegments>false</hasSegments>
          <hasScenarios>false</hasScenarios>
          <DisplayDateInUSFormat>false</DisplayDateInUSFormat>
        </Cell>
      </Cells>
      <OriginalInstanceReportColumns />
      <ElementDataType>us-types:textBlockItemType</ElementDataType>
      <SimpleDataType>textblock</SimpleDataType>
      <ElementDefenition>Description of the asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. This element may be used for all the disclosures related to asset retirement obligations.</ElementDefenition>
      <ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 143
 -Paragraph 22

</ElementReferences>
      <IsTotalLabel>false</IsTotalLabel>
    </Row>
  </Rows>
  <Footnotes />
  <NumberOfCols>1</NumberOfCols>
  <NumberOfRows>2</NumberOfRows>
  <HasScenarios>false</HasScenarios>
  <MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel>
  <SharesRoundingLevel>UnKnown</SharesRoundingLevel>
  <PerShareRoundingLevel>UnKnown</PerShareRoundingLevel>
  <HasPureData>false</HasPureData>
  <SharesShouldBeRounded>true</SharesShouldBeRounded>
</InstanceReport>
