9. Income per Unit

The following is a summary of basic and diluted income per unit (in thousands, except unit and per unit amounts):


	Year Ended December 31,
	2011		2010		2009
Net income available to common unitholders	$	137,053	$	61,745	$	50,690

Weighted average units outstanding—basic		103,053,004		89,261,172		81,715,226
Potentially dilutive common units:
Stock options		187,834		201,704		138,944
Class C Units (2007 Grant)		15,050		97,761		—
Unvested incentive units		190,771		186,691		—
Excess exchange value of the 2026 Debentures		370,719		1,251,817		931,576

Weighted average units outstanding—diluted		103,817,378		90,999,145		82,785,746

Income per unit:
Basic	$	1.33	$	0.69	$	0.62

Diluted	$	1.32	$	0.68	$	0.61

On or after July 15, 2026, the 2026 Debentures would have been exchangeable at the then-applicable exchange rate for cash (up to the principal amount of the 2026 Debentures) and, with respect to any excess exchange value, into cash, shares of Digital Realty Trust, Inc. common stock or a combination of cash and shares of Digital Realty Trust, Inc. common stock. Pursuant to the terms of the Operating Partnership's agreement of limited partnership, the Operating Partnership would have delivered to Digital Realty Trust, Inc. one common unit for each share of common stock issuable upon exchange of the 2026 Debentures. The 2026 Debentures also would have been exchangeable prior to July 15, 2026, but only upon the occurrence of certain specified events, including if the weighted average common stock price exceeded a specified strike price as of the end of a fiscal quarter. During the year ended December 31, 2011, the remaining 2026 Debentures were redeemed and exchanged. Using the treasury method, 370,719 common units contingently issuable upon settlement of the excess exchange value were included as potentially dilutive common units in determining diluted earnings per unit for the year ended December 31, 2011. During the year ended December 31, 2010, the weighted average common stock price exceeded the strike price of $31.42 per share and for the year ended December 31, 2009, the weighted average common stock price exceeded the strike price of $32.22 per share. Therefore, using the treasury method, 1,251,817 and 931,576 common units contingently issuable upon settlement of the excess exchange value were included as potentially dilutive common units in determining diluted earnings per unit for the years ended December 31, 2010 and 2009, respectively.

We have excluded the following potentially dilutive securities in the calculations above as they would be antidilutive:


	Year Ended December 31,
	2011		2010		2009
Potentially dilutive outstanding stock options		—		—		389,016
Potentially dilutive 2029 Debentures		6,328,234		6,217,841		4,345,228
Potentially dilutive outstanding Class C Units (2007 Grant)		—		—		685,036
Potentially dilutive Series C Cumulative Convertible Preferred Units		3,016,780		3,671,190		3,617,214
Potentially dilutive Series D Cumulative Convertible Preferred Units		6,242,257		8,271,022		8,215,220
Potentially dilutive Series E Cumulative Redeemable Preferred Units		1,311,310		—		—

		16,898,581		18,160,053		17,251,714