In July 2011, we adopted the U.S. Silica Holdings, Inc. 2011 Incentive Compensation Plan (the “2011 Plan”), which was amended and restated in May 2015. The 2011 Plan provides for grants of stock options, restricted stock, performance share units and other incentive-based awards. We believe our 2011 Plan aligns the interests of our employees and directors with those of our common stockholders. At March 31, 2020, we have 673,336 shares of common stock that may be issued under the 2011 Plan. We use a combination of treasury stock and new shares if necessary to satisfy option exercises or vesting of restricted awards and performance share units.



	Number of Shares	Weighted Average Exercise Price		Aggregate Intrinsic Value		Weighted Average Remaining Contractual Term in Years
Outstanding at December 31, 2019	826,658	$	28.97	$	11,557	4.1 years
Granted	—	$	—	$	—
Exercised	—	$	—	$	—
Forfeited	—	$	—	$	—
Expired	—	$	—	$	—
Outstanding at March 31, 2020	826,658	$	28.97	$	—	3.9 years
Exercisable at March 31, 2020	826,658	$	28.97	$	—	3.9 years

There were 0 and 10,000 stock options exercised during the three months ended March 31, 2020 and 2019, respectively. The total intrinsic value of stock options exercised was $12 thousand for the three months ended March 31, 2019. Cash received from stock options exercised during the three months ended March 31, 2019 was $128 thousand. The tax benefit realized from stock option exercises was $3 thousand for the three months ended March 31, 2019.

As of March 31, 2020 and 2019, there was no unrecognized compensation expense related to these options. We account for forfeitures as they occur.

The following table summarizes the status of, and changes in, our unvested restricted stock awards during the three months ended March 31, 2020:



	Number of Shares		Grant Date Weighted Average Fair Value
Unvested, December 31, 2019	1,020,248		$	15.86
Granted	900,852		$	5.56
Vested	(245,004	)	$	13.96
Forfeited	(96,467	)	$	14.61
Unvested, March 31, 2020	1,579,629		$	10.35

We granted 900,852 restricted stock and restricted stock unit awards during the three months ended March 31, 2020. We granted 732,860 restricted stock and restricted stock unit awards during the three months ended March 31, 2019. The fair value of the awards was based on the market price of our stock at date of grant.

Our Board of Directors approved and amendment and restatement of the 2011 Plan, effective February 1, 2020, subject to shareholder approval at our 2020 annual meeting of shareholders (the "Annual Meeting"). The amendment increases the current share reserve by 4.025 million shares. During the three months ended March 31, 2020, we granted 834,677 restricted stock units to our executive employees, subject to stockholder approval of the amendment of the 2011 Plan at the Annual Meeting. If this proposal is not approved at the Annual Meeting, these awards will be settled in cash rather than equity.

We recognized $1.5 million of equity-based compensation expense related to restricted stock awards during the three months ended March 31, 2020. We recognized $2.3 million of equity-based compensation expense related to restricted stock awards during the three months ended March 31, 2019. As of March 31, 2020, there was $12.2 million of unrecognized compensation expense related to these restricted stock awards, which is expected to be recognized over a weighted-average period of 2.1 years.

We also granted 315,931 awards during the three months ended March 31, 2020. These awards will vest over a period of one to three years and will be settled in cash. As such, these awards have been classified as liability instruments. We recognized $39 thousand of expense related to these awards for the three months ended March 31, 2020. The liability for these

awards is included in accounts payable and other accrued expenses on our balance sheets. These awards will be remeasured at fair value each reporting period with resulting changes reflected in our income statements. Estimated unrecognized expense related to these awards is $0.5 million over a period of 2.9 years.

The following table summarizes the status of, and changes in, our performance share unit awards during the three months ended March 31, 2020:



	Number of Shares		Grant Date Weighted Average Fair Value
Unvested, December 31, 2019	838,722		$	18.00
Granted	1,020,161		$	9.94
Vested	—		$	—
Forfeited/Cancelled	(121,083	)	$	37.12
Unvested, March 31, 2020	1,737,800		$	13.90

We granted 1,020,161 performance share units during the three months ended March 31, 2020. We granted 607,130 performance share units during the three months ended March 31, 2019. The grant date fair value for these awards was estimated using a Monte Carlo simulation model. The Monte Carlo simulation model requires the use of highly subjective assumptions. Our key assumptions in the model included the price and the expected volatility of our common stock and our self-determined peer group companies’ stock, risk-free rate of interest, dividend yields and cross-correlations between our common stock and our self-determined peer group companies' stock.

We recognized $1.3 million of compensation expense related to performance share unit awards during the three months ended March 31, 2020. We recognized $1.7 million of compensation expense related to performance share unit awards during the three months ended March 31, 2019. As of March 31, 2020, there was $16.6 million of unrecognized compensation expense related to these performance share unit awards, which is expected to be recognized over a weighted-average period of 2.3 years.

We also granted 870,275 awards during the three months ended March 31, 2020. These awards will vest over a period of one to three years and will be settled in cash. As such, these awards have been classified as liability instruments. We recognized $0.7 million of expense related to these awards for the three months ended March 31, 2020. The liability for these awards is included in accounts payable and other accrued expenses on our balance sheets. These awards will be remeasured at fair value each reporting period with resulting changes reflected in our income statements. Estimated unrecognized expense related to these awards is $13.6 million over a period of 2.9 years.