<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><Version>2.2.0.25</Version><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><ReportLongName>11501 - Disclosure - Tenant Leases</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelColumn>false</LabelColumn><CurrencyCode>USD</CurrencyCode><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName>1/1/2010 - 12/31/2010
USD ($)

USD ($) / shares

</KeyName><CurrencySymbol>$</CurrencySymbol><contextRef><ContextID>Duration_1_1_2010_To_12_31_2010</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0001067063</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2010-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2010-12-31T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS><UnitProperty><UnitID>Unit1</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>Unit13</UnitID><UnitType>Divide</UnitType><NumeratorMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></NumeratorMeasure><DenominatorMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></DenominatorMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>Unit12</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty></UPS><CurrencyCode>USD</CurrencyCode><OriginalCurrencyCode>USD</OriginalCurrencyCode></MCU><CurrencySymbol>$</CurrencySymbol><Labels><Label Id="1" Label="12 Months Ended" /><Label Id="2" Label="Dec. 31, 2010" /></Labels></Column></Columns><Rows><Row><Id>2</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_LeasesAbstract</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><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole /><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><NonNumericTextHeader /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>No definition available.</ElementDefenition><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Tenant Leases</Label></Row><Row><Id>3</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_LeasesOfLessorDisclosureTextBlock</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><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terselabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&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 valign="top"&gt;&lt;td style="width: 18pt;" align="right"&gt;

&lt;div&gt;&lt;font style="display: inline; font-family: Times New Roman; font-size: 10pt; font-weight: bold;" class="_mt"&gt;16.&amp;nbsp;&amp;nbsp;&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td&gt;

&lt;div style="text-indent: 0pt; 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;" class="_mt"&gt;&lt;font style="display: inline; text-decoration: underline;" class="_mt"&gt;TENANT LEASES&lt;/font&gt;&lt;/font&gt;&lt;/div&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="justify"&gt;&lt;font style="display: inline; font-family: Times New Roman; font-size: 10pt;" class="_mt"&gt;The Properties are leased to tenants under operating leases with various expiration dates through 2030.&amp;nbsp;&amp;nbsp;Substantially all of the leases provide for annual base rents plus recoveries and escalation charges based upon the tenant's proportionate share of and/or increases in real estate taxes and certain operating costs, as defined, and the pass-through of charges for electrical usage.&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="justify"&gt;&lt;font style="display: inline; font-family: Times New Roman; font-size: 10pt;" class="_mt"&gt;Future minimum rentals to be received under non-cancelable operating leases at December 31, 2010 are as follows &lt;font style="font-style: italic; display: inline;" class="_mt"&gt;(dollars in thousands)&lt;/font&gt;:&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 style="border-bottom: black 2px solid;" valign="top" width="40%"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: -18pt;" align="justify"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;Year&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 2px solid; text-align: right;" valign="top" width="40%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 18pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;Amount&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="40%"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: -18pt;" align="justify"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;2011&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="text-align: right;" valign="top" width="40%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 18pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&lt;font style="margin-left: 165.6pt;" class="_mt"&gt; &lt;/font&gt;$584,959&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="40%"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: -18pt;" align="justify"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;2012&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="40%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 18pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;536,151&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="40%"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: -18pt;" align="justify"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;2013&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="40%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 18pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;457,869&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="40%"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: -18pt;" align="justify"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;2014&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="40%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 18pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;388,291&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="40%"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: -18pt;" align="justify"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;2015&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td valign="top" width="40%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 18pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;321,026&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td style="border-bottom: black 2px solid;" valign="top" width="40%"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: -18pt;" align="justify"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;2016 and thereafter&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 2px solid;" valign="top" width="40%" align="right"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 18pt;" align="right"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;1,064,569&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td valign="top" width="40%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;
&lt;td valign="top" width="40%"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&amp;nbsp; &lt;/font&gt;&lt;/td&gt;&lt;/tr&gt;
&lt;tr&gt;&lt;td style="border-bottom: black 3px double;" valign="top" width="40%"&gt;

&lt;div style="text-indent: 0pt; display: block; margin-left: 0pt; margin-right: -18pt;" align="justify"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;Total&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;
&lt;td style="border-bottom: black 3px double; text-align: right;" valign="top" width="40%"&gt;

&lt;div style="text-align: right; text-indent: 0pt; display: block; margin-left: 0pt; margin-right: 18pt;"&gt;&lt;font style="display: inline; font-family: times new roman; font-size: 10pt;" class="_mt"&gt;&lt;font style="margin-left: 165.6pt;" class="_mt"&gt; &lt;/font&gt;$3,352,865&lt;/font&gt;&lt;/div&gt;&lt;/td&gt;&lt;/tr&gt;&lt;/table&gt;&lt;/div&gt; &lt;/div&gt;</NonNumbericText><NonNumericTextHeader>16.&amp;nbsp;&amp;nbsp;


TENANT LEASES



The Properties are leased to tenants under operating leases with various expiration dates through</NonNumericTextHeader><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>us-types:textBlockItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>Description and amounts of lessor entity's leasing arrangements for operating, capital and leveraged leases. This element can be used to disclose the entity's entire lease disclosure as a single block of text.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 13
 -Paragraph 23

</ElementReferences><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Tenant Leases</Label></Row></Rows><Footnotes /><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows><ReportName>Tenant Leases</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>false</HasCustomUnits><SharesShouldBeRounded>true</SharesShouldBeRounded></InstanceReport>
