Stock Based Compensation (Tables)

12 Months Ended

Dec. 31, 2014

Summary of Option Activities

A summary of Portola’s stock option activity follows:

				Shares
				Subject to			Weighted-
	Shares Available			Outstanding			Average Exercise
	for Grant			Options			Price Per Share
Balance at December 31, 2013		81,948			3,708,773		$	9.43
Options authorized		2,045,785		–			–
Options granted		(1,358,013	)		1,358,013			25.96
Options exercised	–				(652,125	)		6.68
Options canceled		165,493			(165,493	)		18.86
Balance at December 31, 2014		935,213			4,249,168		$	14.77

Additional Information Related to the Status of Options

Additional information related to the status of options at December 31, 2014, is as follows (aggregate intrinsic value in thousands):

			Weighted-
			Average		Remaining
			Exercise Price		Contractual		Aggregate
	Shares		Per Share		Life		Intrinsic Value
Outstanding		4,249,168	$	14.77		6.6	$	57,709
Vested and expected to vest		4,106,671	$	14.47		6.6	$	57,009
Vested		2,503,676	$	9.67		5.2	$	46,722

Stock Options Outstanding and Vested and Exercisable

Additional information regarding our stock options outstanding and vested and exercisable as of December 31, 2014 is summarized below:

	Options Outstanding				Options Vested
		Weighted
		Average	Weighted		Number	Weighted
	Number of	Remaining	Average		of	Average
	Options	Contractual	Exercise Price		Options	Exercise Price
Exercise Prices	Outstanding	Life (Years)	per Share		Vested	Per Share
$1.00 - $5.10	945,481	2.8	$	4.21	945,481	$	4.21
$5.30 -  $9.00	1,068,191	6.0		8.07	927,581		8.21
$9.50 - $23.85	976,963	8.2		17.61	406,830		16.81
$24.39 - $26.67	861,050	8.6		25.13	178,702		25.04
$26.75 - $29.19	397,483	9.5		28.42	45,082		29.02
	4,249,168	6.6	$	14.77	2,503,676	$	9.67

Classification of Stock-Based Compensation Expense

Stock-based compensation expense, net of estimated forfeitures, is reflected in the consolidated statements of operations as follows (in thousands):

	Year Ended December 31,
	2014		2013		2012
Research and development	$	4,551	$	2,295	$	1,452
General and administrative		4,782		2,679		1,357
Total stock-based compensation	$	9,333	$	4,974	$	2,809

Employee Stock Option

Fair Values of Employee Stock Options

The following table illustrates the weighted-average assumptions for the Black-Scholes option-pricing model used in determining the fair value of options granted to employees:

	Year Ended December 31,
	2014	2013		2012
Risk-free interest rate	1.81% - 1.89%		1.43%		1.10%
Expected life	6.0 years	6.0 years		6.0 years
Expected volatility	69% - 80%		79%		72%
Dividend yield	–	–		–

Employee Stock Purchase Plan

Fair Values of Employee Stock Options

The following table illustrates the weighted-average assumptions for the Black-Scholes option-pricing model used in determining the fair value of ESPP purchase rights granted to employees:

	Year Ended December 31,
	2014		2013
Risk-free interest rate		0.08%		0.10%
Expected life	0.5 years		0.4 years
Expected volatility		73%		62%
Dividend yield	–		–