As of September 30, 2017, there were stock options outstanding under the Company’s 1995 Stock Option Plan, Second Amended and Restated 1997 Stock Option Plan, 1999 Stock Option Plan and the 2011 Company Incentive Plan. All four plans were approved by the shareholders. The 1995 Stock Option Plan and the 1999 Stock Option Plan have expired, and no further options may be granted under those plans. During fiscal 2009, the Second Amended and Restated 1997 Stock Option Plan was amended to make an additional 592,000 options available for granting and as of September 30, 2013 there were no shares available for issuance under the Amended and Restated 1997 Stock Option Plan. As of September 30, 2017, there were no shares available for issuance under the 2011 Company Incentive Plan. The plans granted specified numbers of options to non-employee directors, and they authorized the Compensation Committee of the Board of Directors to grant either incentive or non-statutory stock options to employees. Vesting periods are established by the Compensation Committee at the time of grant. All stock options outstanding as of September 30, 2017 and September 30, 2016 were non-statutory stock options, had exercise prices equal to the market price on the date of grant, and had expiration dates ten years from the date of grant.

On July 23, 2013, the Board of Directors approved the Company’s 2013 Incentive Stock Plan (the “2013 Plan”), and resolved to cease issuing securities under all prior Company equity compensation plans. The 2013 Plan was approved by the Company’s shareholders at the Annual Meeting of Stockholders on September 9, 2013. The purpose of the 2013 Plan is to provide additional incentives to select persons who can make, are making, and continue to make substantial contributions to the growth and success of the Company, to attract and retain the employment and services of such persons, and to encourage and reward such contributions, by providing these individuals with an opportunity to acquire or increase stock ownership in the Company through either the grant of options or restricted stock. The 2013 Plan is administered by the Compensation Committee or such other committee as is appointed by the Board of Directors pursuant to the 2013 Plan (the “Committee”). The Committee has full authority to administer and interpret the provisions of the 2013 Plan including, but not limited to, the authority to make all determinations with regard to the terms and conditions of an award made under the 2013 Plan. The maximum number of shares that may be granted under the 2013 Plan is 1,000,000. This number is subject to adjustment to reflect changes in the capital structure or organization of the Company.

On August 16, 2017 the Stockholders approved an amendment to the Company’s 2013 Incentive Stock Plan to increase the number of shares available for issuance pursuant to awards granted under the Plan from 1,000,000 shares to 4,000,000 shares.

A summary of stock option activity is as follows:

Stock options outstanding as of September 30, 2017 were as follows (number of options in thousands):

As of September 30, 2017, the aggregate intrinsic value of outstanding stock options and exercisable stock options was approximately $461,000 and $303,000, respectively.

The average fair value of stock options granted was estimated to be $4.63 per share in fiscal 2017 and $7.00 per share in fiscal 2017 and 2016, respectively. This estimate was made using the Black-Scholes option pricing model and the following weighted average assumptions:

Stock-based compensation expense attributable to stock options was $902,000 and $793,000 in 2017 and 2016, respectively. As of September 30, 2017, there was approximately $2,178,000 of unrecognized compensation expense related to unvested stock options outstanding, and the weighted average vesting period for those options was 3.5 years.