At September 30, 2012, we have instruments outstanding under two stock-based compensation plans; the 1996 Stock Incentive Plan (the 1996 Plan) and the Fourth Amended and Restated 2002 Stock Incentive Plan (the 2002 Plan). Currently, under the 2002 Plan, we may grant incentive stock options, nonqualified stock options, and restricted stock awards to full-time employees and directors, and nonqualified stock options and restricted stock awards may be granted to our consultants and agents. Total shares authorized under each plan are 1.5 million shares and 12 million shares, respectively. Although instruments are still outstanding under the 1996 Plan, the plan has expired and no new grants may be made from it. Under both plans, the exercise price of each option is greater than or equal to the closing market price of our common stock on the day prior to the date of the grant.

Stock options granted under the 1996 Plan and the 2002 Plan generally vest on an annual basis over one to four years. Outstanding stock options under the plans, if not exercised, generally expire ten years from their date of grant or 90 days from the date of an optionee's separation from employment with the Company. We issue new shares of our common stock upon exercise of stock options.

Stock-based payments to employees and directors, including grants of stock options, are recognized in the consolidated statement of operations based on their estimated fair values. The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option pricing model. Expected volatilities are based on the Company's historical volatility, which management believes represents the most accurate basis for estimating expected future volatility under the current circumstances. Navidea uses historical data to estimate forfeiture rates. The expected term of stock options granted is based on the vesting period and the contractual life of the options. The risk-free rate is based on the U.S. Treasury yield in effect at the time of the grant.

Compensation cost arising from stock-based awards is recognized as expense using the straight-line method over the vesting period. Restricted shares may vest based on the passage of time, or they may vest upon occurrence of a specific event or achievement of goals as defined in the grant agreements. In such cases, we record compensation expense related to grants of restricted stock based on management's estimates of the probable dates of the vesting events.

For the three-month periods ended September 30, 2012 and 2011, our total stock-based compensation expense was approximately $588,000 and $1.8 million, respectively. For the nine-month periods ended September 30, 2012 and 2011, our total stock-based compensation expense was approximately $1.7 million and $3.1 million, respectively. Stock-based compensation expense for the first nine months of 2011 included approximately $1.5 million of expense related to the separation of our former President and CEO. (See Note 7.) We have not recorded any income tax benefit related to stock-based compensation in any of the three-month or nine-month periods ended September 30, 2012 and 2011.

A summary of the status of our stock options as of September 30, 2012, and changes during the nine-month period then ended, is presented below:

A summary of the status of our unvested restricted stock as of September 30, 2012, and changes during the nine-month period then ended, is presented below:

As of September 30, 2012, there was approximately $2.3 million of total unrecognized compensation expense related to unvested stock-based awards, which we expect to recognize over remaining weighted average vesting terms of 1.9 years.