11. STOCK-BASED COMPENSATION

In April 2014, the Company adopted its Equity Incentive Plan (the “Plan”), reserving 1,351,000 shares of common stock for grants to employees, officers, directors and consultants. During April 2017, the Plan was amended and restated whereby an additional 1,500,000 shares of common stock and 100,000 shares of Series A Preferred Stock were added to the plan for future issuance. During June 2018, the Company’s shareholders approved the addition of 200,000 preferred shares to the Plan for future grants. As of June 30, 2019, 554,910 shares of common stock and 138,400 shares of Series A Preferred Stock are available for grant under the Plan. Permissible awards include incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock, RSUs, performance stock and cash-settled awards and other stock-based awards in the discretion of the Compensation Committee of the Board of Directors including unrestricted stock grants.

The common stock equity based RSUs contain a common provision in which the units shall immediately vest and become converted into common shares at the rate of one share per RSU, immediately after a change in control, as defined in the award agreement. The preferred stock RSUs contain a similar provision, which vest and convert to Series A Preferred Stock upon a change in control.

Common and preferred stock RSUs

In February 2019, the Compensation Committee approved executive bonuses to be paid in shares of Series A Preferred Stock, with the number of shares and the amount based on specified criteria being achieved during the year 2019. The actual amount will be settled in early 2020 based on the achievement of the specified criteria. For the three and six months ended June 30, 2019, an expense of approximately $301,000 and $602,000, respectively, was recorded for these bonuses based on the value of the shares at the grant date and recognized over the service period. The portion of the stock compensation expense to be used for the payment of withholding and payroll taxes is included in accrued compensation in the condensed consolidated balance sheets. The balance of the stock compensation expense has been recorded as additional paid-in capital.

The following table summarizes the RSU transactions related to the common and preferred stock under the Equity Incentive Plan for the six months ended June 30, 2019:

Of the total outstanding and unvested common stock RSUs at June 30, 2019, 568,081 RSUs are classified as equity and 34,333 RSUs are classified as a liability. All of the preferred stock RSUs are classified as equity.

Stock-based compensation expense

The Company recognizes compensation expense on a straight-line basis over the total requisite service period for the entire award. For stock awards classified as equity, the market price of our common stock or preferred stock on the date of grant is used in recording the fair value of the award and includes the related taxes. For stock awards classified as a liability, the earned amount is marked to market based on the end of period common stock price. The liability for the cash-settled awards was approximately $479,000 and $118,000 at June 30, 2019 and December 31, 2018, respectively, and is included in accrued compensation in the condensed consolidated balance sheets.

The following table summarizes the components of share-based compensation expense for the three and six months ended June 30, 2019 and 2018: