Compensation cost for PSUs that have a service condition and a market condition and are accounted for as equity awards is measured based on the grant date estimated fair value and recognized over the vesting period on a straight-line basis. The grant date estimated fair value is determined using a Monte Carlo simulation model. Compensation cost for PSUs that have a service condition and a performance condition and are accounted for as equity awards is initially measured based on the grant date fair value. Cumulative compensation cost is subsequently adjusted at the end of each reporting period to reflect the current estimation of achieving the performance condition. For the three- and nine-month periods ended September 30, 2021, $1.0 million and $3.1 million, respectively, were recognized as share-based compensation related to equity PSUs. For the three- and nine-month periods ended September 30, 2020, $1.0 million and $3.0 million, respectively, were recognized as share-based compensation related to equity PSUs. In January 2021, based on the performance of our common stock price as compared to our performance peer group over a three-year period, 368,038 equity PSUs granted in 2018 vested at 200%, representing 736,075 shares of our common stock with a total market value of $3.1 million.
RSUs granted in 2021 have been accounted for as liability awards. Liability RSUs are measured at their estimated fair value at each balance sheet date, and subsequent changes in the fair value of the awards are recognized in earnings for the portion of the award for which the requisite service period has elapsed. Cumulative compensation cost for vested liability RSUs equals the actual payout value upon vesting. Compensation cost recognized for the three-month period ended September 30, 2021 was minimal. For the nine-month period ended September 30, 2021, $0.4 million was recognized as compensation cost.
In 2021 and 2020, we granted fixed-value cash awards of $3.5 million and $4.7 million, respectively, to select management employees under the 2005 Incentive Plan. The value of these cash awards is recognized on a straight-line basis over a vesting period of three years. For the three- and nine-month periods ended September 30, 2021, $1.0 million and $3.0 million, respectively, were recognized as compensation cost. For the three- and nine-month periods ended September 30, 2020, $1.1 million and $3.4 million, respectively, were recognized as compensation cost.
Defined Contribution Plan
We sponsor a defined contribution 401(k) retirement plan. We suspended our discretionary contributions for an indefinite period beginning January 2021.
Employee Stock Purchase Plan
We have an employee stock purchase plan (the “ESPP”). As of September 30, 2021, 1.6 million shares were available for issuance under the ESPP. The ESPP currently has a purchase limit of 260 shares per employee per purchase period.
For more information regarding our employee benefit plans, including the 2005 Incentive Plan and the ESPP, see Note 14 to our 2020 Form 10-K.
Note 10 — Business Segment Information
We have 3 reportable business segments: Well Intervention, Robotics and Production Facilities. Our U.S., U.K. and Brazil well intervention operating segments are aggregated into the Well Intervention segment for financial reporting purposes. Our Well Intervention segment provides services enabling our customers to safely access offshore wells for the purpose of performing production enhancement or decommissioning operations primarily in the Gulf of Mexico, Brazil, the North Sea and West Africa. Our well intervention vessels include the Q4000, the Q5000, the Q7000, the Seawell, the Well Enhancer, and the Siem Helix 1 and Siem Helix 2 chartered vessels. Our well intervention equipment includes IRSs, SILs and the ROAM, some of which we provide on a stand-alone basis. Our Robotics segment provides offshore construction, trenching, seabed clearance, inspection, repair and maintenance services to both the oil and gas and the renewable energy markets globally. Our Robotics services also complement well intervention services. Our Robotics segment includes ROVs, trenchers, a ROVDrill and 2 robotics support vessels under long-term charter, the Grand Canyon II and the Grand Canyon III, as well as spot vessels as needed. Our Production Facilities segment includes the HP I, the HFRS and our ownership of oil and gas properties (Note 11). All material intercompany transactions between the segments have been eliminated.