Incentive Plans

Stock-based compensation. For the three and six months ended June 30, 2017, the Company recorded $27 million and $57 million, respectively, of stock-based compensation expense for all plans, as compared to $29 million and $53 million for the same respective periods in 2016. As of June 30, 2017, there was $137 million of unrecognized stock-based compensation expense related to unvested share-based compensation plans, including $31 million attributable to stock-based awards that are expected to be settled on their vesting date in cash, rather than in equity shares ("Liability Awards"). The unrecognized compensation expense will be recognized on a straight-line basis over the remaining vesting periods of the awards, which is a period of less than three years on a weighted average basis. As of June 30, 2017 and December 31, 2016, accounts payable – due to affiliates included $10 million and $22 million, respectively, of liabilities attributable to Liability Awards.

The following table summarizes the activity that occurred during the six months ended June 30, 2017 for each type of share-based incentive award issued by Pioneer:



	Restricted Stock Equity Awards		Restricted Stock Liability Awards		Performance Units	Stock Options
Outstanding as of December 31, 2016	1,077,227		290,552		178,556	159,378
Awards granted	320,103		108,911		59,044	—
Awards forfeited	(13,527	)	(5,012	)	—	—
Awards vested	(437,845	)	(129,499	)	—	—
Outstanding as of June 30, 2017	945,958		264,952		237,600	159,378