Total share-based compensation related to stock options, common stock awards, and non-financing warrants was $0.7 million and $0.3 million during the three months ended March 31, 2017 and 2016, respectively.

Share-based compensation expense is classified in the condensed consolidated statements of operations as follows:

Employee Stock Options

During the three months ended March 31, 2017, the Company granted 175,000 employee stock options. The key valuation assumptions used consisted of the Company’s stock price, a risk free rate of 0.19% and an expected volatility of 110%. During the three months ended March 31, 2016, the Company granted 12,122 employee stock options. The key valuation assumptions used consisted of the Company’s stock price, a risk free rate of 0.54% and an expected volatility of 123%. During the three months ended March 31, 2017 and 2016, the Company extended the exercise expiration date of certain former employee stock option awards resulting in a change in incremental value of approximately $4,000 and $24,000, respectively, which was charged to administrative expense. The Company recognized a total of $0.6 million and $0.5 million of compensation expense related to employee stock options during the three months ended March 31, 2017 and 2016, respectively.

Non-Employee Stock Options

No non-employee stock options were granted and no non-employee stock options were exercised during the three months ended March 31, 2017 or 2016. The Company recognized $43,873 and ($971) of compensation expense related to non-employee stock options during the three months ended March 31, 2017 and 2016, respectively.

Common Stock Awards

During the three months ended March 31, 2017 and 2016, the Company granted 5,475 and 8,641 common stock awards, respectively, based on the value of the services provided and the average stock price during each respective quarter. As all services were rendered in each respective quarter, $31,068 and $57,790 of compensation expense related to common stock awards was recognized during each of the three month periods ended March 31, 2017 and 2016, respectively. All common stock awards were authorized but not issued as of March 31, 2017.

Warrants

In connection with certain of the Company’s collaboration agreements and consulting arrangements, the Company has issued warrants to purchase shares of common stock as payment for services. As of March 31, 2017 and December 31, 2016, warrants to purchase 646,249 shares of common stock were outstanding. The fair value of these warrants were determined at each issuance date using the Black-Scholes option pricing model. The warrants are subject to re-measurement at each reporting period until the measurement date is reached. Expense is recognized on a straight-line basis over the expected service period or at the date of issuance, if there is not a service period. The Company recognized a gain of $0.02 million on revaluation of warrants for the three months ended March 31, 2017. During the three months ended March 31, 2016, the Company recognized a gain of $0.2 million as a result of a reduction in estimated fair value of warrants. No warrants were issued in connection with collaboration agreements and consulting services during the three months ended March 31, 2017 and 2016.