9. Stock Based Compensation

In January 2013, our Board of Directors adopted our 2013 Equity Incentive Plan (the “2013 Plan”), which became effective upon the closing of our initial public offering in May 2013. On January 1, 2017, the number of shares available for issuance under the 2013 Plan automatically increased by a number of shares equal to 5% of the total common stock outstanding at December 31, 2016. In September 2017, our Board of Directors adopted an Inducement Plan with 1,500,000 shares available for issuance to new employees entering into employment with Portola in accordance with NASDAQ Listing Rule 5635(c)(4) (the “2017 Plan”). As of September 30, 2017, there were 15,032,633 shares reserved under the 2013 Plan and 1,500,000 shares reserved under the 2017 Plan for the future issuance of equity awards.

Stock Options

The following table summarizes stock option activity under our 2013 Plan and 2017 Plan and related information during the nine months ended September 30, 2017:

	Shares
	Subject to			Weighted-
	Outstanding			Average Exercise
	Options			Price Per Share
Balance at December 31, 2016		5,817,116		$	25.26
Options granted		1,813,300			38.68
Options exercised		(1,008,791	)		15.37
Options canceled		(200,522	)		35.48
Balance at September 30, 2017		6,421,103		$	30.28

Performance Stock Options (“PSOs”)

In May 2016, the Compensation Committee of our Board of Directors approved the commencement of granting performance stock option awards to our executive and senior officers. PSOs represent a contingent right to purchase our Common Stock upon achievement of specified conditions. The PSOs granted in May 2016 will vest upon the achievement of certain regulatory and manufacturing goals related to our lead programs. As of September 30, 2017, 90,378 shares subject to outstanding PSOs were unvested and there was $0.3 million of unrecognized compensation costs relates to these PSOs. Management currently estimates the vesting of these PSOs to be probable of vesting and will be recognized over a weighted-average period of 0.41 years.

The following table summarizes PSO activity under our 2013 Plan and related information during the nine months ended September 30, 2016:

	Shares
	Subject to			Weighted-
	Outstanding			Average Exercise
	Options			Price Per Share
Balance at December 31, 2016		180,752		$	23.76
Options granted		—			—
Options exercised		(4,635	)		—
Options canceled		—			—
Balance at September 30, 2017		176,117		$	23.76

Restricted Stock Units (“RSUs”)

In January 2015, the Compensation Committee of our Board of Directors approved the commencement of granting restricted stock units, to our employees. RSUs are share awards that entitle the holder to receive freely tradable shares of our Common Stock upon vesting.

The following table summarizes RSU activity, under our 2013 Plan and related information:

	Shares
	Subject to			Weighted-
	Outstanding			Average grant date
	RSUs			fair value per share
Balance at December 31, 2016		546,507		$	28.38
RSUs granted		338,800			26.80
RSUs released		(211,882	)		28.26
RSUs canceled		(35,653	)		27.25
Balance at September 30, 2017		637,772		$	27.65

Performance Stock Units (“PSUs”)

In January 2015, the Compensation Committee of our Board of Directors approved the commencement of granting performance stock units to our employees. PSUs are share awards that entitle the holder to receive freely tradable shares of our Common Stock upon achievement of specified conditions. In January 2016, the Compensation Committee of our Board of Directors approved a program to award up to 102,906 PSUs to the management team based on the achievement of certain commercial and regulatory goals related to andexanet alfa and betrixaban, respectively. In January 2017, the Compensation Committee of our Board of Directors approved a program to award up to 143,750 PSUs to the management team based on the achievement of certain regulatory goals related to andexanet alfa.

The following table summarizes PSU activity, under our 2013 Plan and related information:

	Shares
	Subject to			Weighted-
	Outstanding			Average grant date
	PSUs			fair value per share
Balance at December 31, 2016		285,866		$	29.24
PSUs granted		143,750			25.54
PSUs released		(60,374	)		35.97
PSUs canceled		(52,281	)		33.76
Balance at September 30, 2017		316,961		$	25.53

The table below sets forth the functional classification of stock-based compensation expense, for the periods presented (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development	$	4,155	$	3,465	$	14,974	$	9,561
Selling, general and administrative		5,960		4,307		17,431		12,903
Total stock-based compensation	$	10,115	$	7,772	$	32,405	$	22,464