We have stock option and stock incentive plans for employees and non-employee Directors that provide for grants of restricted stock awards (“RSAs”), restricted stock units (“RSUs”), performance stock units (“PSUs”), and options to purchase shares of our common stock at exercise prices generally equal to the fair value of such stock at the dates of grant. We also maintain a shareholder-approved Employee Stock Purchase Plan (“ESPP”) for the benefit of our employees. The ESPP allows eligible employees to purchase common stock on a regular basis at the lower of 85% of the market price at the beginning or end of each offering period.

During the three months ended March 31, 2022 the Compensation Committee of our Board of Directors (the “Committee”) authorized awards from approved stock incentive plans of RSUs and PSUs to certain employees and company officers, which, assuming that performance under the PSUs were to be achieved at target levels, together totaled 452,000 shares and had an aggregate grant date market value of $8.3 million.

During the three months ended March 31, 2021 the Committee authorized awards from approved stock incentive plans of RSUs and PSUs to certain employees, and RSAs and PSUs to certain Company officers, which, assuming that performance under the PSUs were to be achieved at target levels, together totaled 381,000 shares and had an aggregate grant date market value of $9.5 million.

The Committee authorized, from approved stock incentive plans, grants of stock options to purchase a total of 314,000 and 226,000 shares to certain Company officers during the three months ended March 31, 2022 and 2021, respectively. The exercise prices of the options were equal to the closing stock prices on their respective grant dates.

Employees purchased common stock totaling 37,000 and 36,000 shares in the three months ended March 31, 2022 and 2021, respectively, through the ESPP.

The following weighted-average assumptions were used to determine the fair value of options and shares purchased under the ESPP:


	Three Months Ended
	March 31, 2022
	Stock Options	ESPP
Expected life	5.0 Years	0.5 Years
Expected stock price volatility	0.40	0.31
Risk-free interest rate	1.89%	0.22%

The following table summarizes total stock compensation expenses prior to the capitalization of amounts into Deferred preservation and Inventory costs (in thousands):


	Three Months Ended
	March 31,
	2022		2021
RSA, RSU, and PSU expense	$	2,768	$	2,050
Stock option and ESPP expense		572		587
Total stock compensation expense	$	3,340	$	2,637

Included in the total stock compensation expense, as applicable in each period, were expenses related to RSAs, RSUs, PSUs, and stock options issued in each respective year, as well as those issued in prior periods that continue to vest during the period, and compensation related to the ESPP. These amounts were recorded as stock compensation expense and were subject to our normal allocation of expenses to inventory costs and deferred preservation costs. We capitalized $174,000 and $157,000 in the three months ended March 31, 2022 and 2021, respectively, of the stock compensation expense into our inventory costs and deferred preservation costs.