Historically, stock options have been granted with an exercise price equal to the market value of the common stock on the date of grant, with expiration 10 years from the date they are granted, and generally vest over a one to three-year period for employees and members of the Board. Upon exercise, new shares will be issued by the Company. The restricted shares and restricted stock units (“RSUs”) granted to Board members and employees generally have a three-year graded vesting period and are subject to accelerated vesting and forfeiture under certain circumstances.

The following table provides the weighted average assumptions used in determining the fair value of the stock option awards granted during the three-month periods ended March 31, 2021 and 2020.

During March 2021, the Company granted 312,500 stock options with an exercise price of $6.00 and 152,500 RSUs. The market value of the Company’s common stock was $5.00 at the grant date of these awards. The Company recognized approximately $0.3 million and $0.4 million of stock-based compensation expense during the three-month periods ended March 31, 2021 and 2020, respectively.