NATURAL GAS SERVICES GROUP INC

15. Stock-Based and Other Long-Term Incentive Compensation

We maintain the stockholder-approved 2019 Equity Incentive Plan, as amended (the “Equity Incentive Plan”) for the issuance of stock-based compensation awards to our employees, certain consultants and Board of Director members. The Equity Incentive Plan provides for a total of 1,650,000 shares of common stock for issuance in the form of awards for: (i) stock options, (ii) stock appreciation rights, (iii) restricted awards in the form of restricted stock and restricted stock units (“RSUs”), (iv) performance share awards, including performance share units (“PSUs”) and (v) other equity-based awards. After consideration of the activity described in detail below, a total of 495,269 shares remained available for grant under the Equity Incentive Plan as of September 30, 2026. The Equity Incentive Plan expires on June 20, 2034. Until its expiration on February 28, 2026, we also maintained the 1998 Stock Option Plan, as amended (the “Stock Option Plan”) through which we issued stock options for all years prior to 2026.

The following table summarizes the total stock-based compensation expense recognized during the periods presented:

(1) Represents compensation expense associated with awards that may be settled in cash at the option of the grantee.

Stock Options

While the Stock Option Plan has expired, all stock options that were outstanding as of December 31, 2025, will remain subject to their vesting rights through their contractual lives. All options granted after 2025, including those indicated below, were granted under the Equity Incentive Plan. A summary of all option activity during the nine months ended September 30, 2026, is presented below:

The following table summarizes information about our stock options outstanding as of September 30, 2026:

The following table summarizes changes in our unvested stock options during the nine months ended September 30, 2026:

As of September 30, 2026, there was a total of approximately $0.5 million of unrecognized compensation cost related to unvested options which is expected to be recognized over the next 1.81 years.

Time-Vested Restricted Stock and Restricted Stock Units

The following table summarizes all restricted stock and RSU activity during the nine months ended September 30, 2026:

As of September 30, 2026, there was a total of approximately $3.1 million of unrecognized compensation cost related to unvested restricted stock and RSUs which is expected to be recognized over the next 1.90 years.

Cash Settled Restricted Stock Units

The 2025 and 2024 grants of RSUs to the independent Board members that can be settled in cash represent liability-classified awards. Compensation expense associated with these awards is based upon the fair value of Common Stock at each reporting period relative to that portion of the service period that has passed. Accordingly, the compensation expense is variable in nature.

The following table summarizes all cash settled RSU activity during the nine months ended September 30, 2026, is presented below:

(1) Of the total awards that vested,4,456 RSUs were settled in cash and the remaining 9,356 RSUs were settled in shares.

Performance Share Units

The potential payout for the PSU awards is based upon performance for athree-year period ending December 31, 2026, for the 2024 grants, December 31, 2027, for the 2025 grants and December 31, 2028, for the 2026 grants measured against relative total shareholder return (“TSR”) compared to a peer group of companies as established by the Compensation Committee. The PSU award payout ranges from zero (if the Company ranks below the 31.25th percentile for the 2024 and 2025 grants and below the 30th percentile for the 2026 grant) and up to 200% (if the Company ranks first) based upon our relative TSR performance ranking (subject to certain caps based on absolute TSR as defined in the PSU agreements).

With respect to vesting, the PSUs have both a service condition and a market condition. Due to the presence of the TSR measurement for the common equity of the peer companies, including the Company’s Common Stock, which is deemed a “market condition,” the grant-date fair values of the PSUs have been determined using a binomial pricing model, or a Monte Carlo simulation model.

The following table summarizes the weighted average grant date fair values of PSUs granted and the assumptions used in the Monte Carlo simulation model for the determination of the grant date fair values of our PSUs granted during the nine months ended September 30, 2026:

The following table summarizes all PSU activity during the nine months ended September 30, 2026:

As of September 30, 2026, there was a total of approximately $2.4 million of unrecognized compensation cost related to the unvested portion of the PSUs which is expected to be recognized over the next 1.47 years.