Parent Company Stock-Based Compensation

GM grants to certain employees and key executive officers Restricted Stock Units (RSUs), Performance-based Share Units (PSUs) and stock options. Shares awarded under the plans are subject to forfeiture if the participant leaves the company for reasons other than those permitted under the plans, such as retirement, death or disability.

RSU awards granted either cliff vest or ratably vest generally over a three-year service period, as defined in the terms for each award. PSU awards vest at the end of a three-year performance period based on performance criteria determined by the Executive Compensation Committee of the GM Board of Directors at the time of award. The number of shares earned may equal, exceed or be less than the targeted number of shares depending on whether the performance criteria are met, surpassed or not met. Stock options expire 10 years from the grant date. GM's performance-based stock options vest ratably over 55 months based on the performance of its common stock relative to that of a specified peer group. GM's service-based stock options vest ratably over 19 months to three years.

The following table summarizes information about RSUs, PSUs and stock options granted to our employees and key executive officers under GM's stock-based compensation programs (units in thousands):



	Year Ended December 31, 2018
	Shares		Weighted-Average Grant Date Fair Value		Weighted-Average Remaining Contractual Term (years)
Units outstanding at January 1, 2018	2,873		$	28.44	1.4
Granted	774		$	38.66
Settled	(664	)	$	33.01
Forfeited or expired	(121	)	$	34.25
Units outstanding at December 31, 2018^(a)	2,862		$	27.54	1.2
Units unvested and expected to vest at December 31, 2018	1,439		$	38.23	1.8
Units vested and payable at December 31, 2018	1,335		$	15.56

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(a)	Includes the target amount of PSUs.

Total compensation expense related to the above awards was $29 million, $48 million and $45 million in 2018, 2017 and 2016.

The assumptions used to estimate the fair value of the stock options issued during 2018 and 2017 are a dividend yield of 3.69% and 4.43%, expected volatility of 28.0% and 25.0%, a risk-free interest rate of 2.73% and 1.97%, and an expected option life of 5.98 and 5.84 years. There were no stock options issued during 2016.

At December 31, 2018, total unrecognized compensation expense for nonvested equity awards granted was $27 million. This expense is expected to be recorded over a weighted-average period of 1.2 years. The total fair value of RSUs and PSUs vested was $21 million, $16 million and $12 million in 2018, 2017 and 2016.

In 2018, 2017, and 2016, total payments for 165,000, 300,000 and 49,000 RSUs settled in cash under stock incentive plans were $7 million, $11 million and $2 million.