23. STOCK-BASED COMPENSATION PLAN

Under the 2016 Stock Incentive Plan, we may grant nonqualified stock options, incentive stock options, stock appreciation rights, restricted stock, phantom stock, performance share units and other stock-based awards to our employees, directors and consultants and to employees and consultants of our subsidiaries, provided that incentive stock options may be granted solely to employees. The terms of the grants under both the 2016 Stock Incentive Plan and the Prior Plan are fixed at the grant date. Initially, there were approximately 8.2 million shares available for issuance under the 2016 Stock Incentive Plan. However, the number of shares available for issuance may be adjusted to include any shares surrendered, exchanged, forfeited or settled in cash pursuant to the Prior Plan. As of December 31, 2023, we had approximately 6 million shares remaining under the 2016 Stock Incentive Plan available for grant. Option awards have a maximum contractual term of 10 years and generally must have an exercise price at least equal to the market price of our common stock on the date the option award is granted. Outstanding stock-based awards generally vest over a three-year period. 

The compensation cost under the 2016 Stock Incentive Plan and the Prior Plan for our Company and Huntsman International were as follows (dollars in millions):

The total income tax benefit recognized in the statement of operations for stock-based compensation arrangements was $3 million, $8 million and $3 million for the years ended December 31, 2023, 2022 and 2021, respectively.

Stock Options

The fair value of each stock option award is estimated on the date of grant using the Black-Scholes valuation model that uses the assumptions noted in the following table. Expected volatilities are based on the historical volatility of our common stock through the grant date. The expected term of options granted was estimated based on the contractual term of the instruments and employees’ expected exercise and post-vesting employment termination behavior. The risk-free rate for periods within the contractual life of the option was based on the U.S. Treasury yield curve in effect at the time of grant. The assumptions noted below represent the weighted averages of the assumptions utilized for all stock options granted during the year. During both of the years ended  December 31, 2023 and 2022, no stock options were granted.

A summary of stock option activity under the 2016 Stock Incentive Plan and the Prior Plan as of December 31, 2023 and changes during the year then ended is presented below:

The weighted-average grant-date fair value of stock options granted during 2021 was $11.48 per option. As of December 31, 2023, there was less than $1 million of total unrecognized compensation cost related to nonvested stock option arrangements granted under the 2016 Stock Incentive Plan and the Prior Plan. That cost is expected to be recognized over a weighted-average period of approximately 0.2 years.

During the years ended December 31, 2023, 2022 and 2021, the total intrinsic value of stock options exercised was approximately $3 million, $12 million and $13 million, respectively. Cash received from stock options exercised during the years ended December 31, 2023, 2022 and 2021 was approximately $5 million, $6 million and $10 million, respectively. The cash tax benefit from stock options exercised during each of the years ended December 31, 2023, 2022 and 2021 was approximately nil, $2 million and $2 million, respectively.

Nonvested Shares

Nonvested shares granted under the 2016 Stock Incentive Plan and the Prior Plan consist of restricted stock and performance share unit awards, which are accounted for as equity awards, and phantom stock, which is accounted for as a liability award because it can be settled in either stock or cash. The fair value of each restricted stock and phantom stock award is estimated to be the closing stock price of Huntsman’s stock on the date of grant.

We grant two types of performance share unit awards. For one type of performance share unit award, the performance criteria are total stockholder return of our common stock relative to the total stockholder return of a specified industry peer group for the three-year performance periods. The fair value of each performance share unit award is estimated using a Monte Carlo simulation model that uses various assumptions, including an expected volatility rate and a risk-free interest rate. For the years ended December 31, 2023, 2022 and 2021, the weighted-average expected volatility rate was 37.6%, 43.5% and 44.9%, respectively, and the weighted average risk-free interest rate was 4.38%, 1.67% and 0.2%, respectively. For the performance share unit awards granted during the year ended December 31, 2023, 2022 and 2021, the number of shares earned varies based upon the Company achieving certain performance criteria over a three-year performance period.

During the first quarter of 2022, we issued a second type of performance award, which also includes a market condition. The performance criteria are our corporate free cash flow achieved relative to targets set by management, modified for the total stockholder return of our common stock relative to the total stockholder return of a specified industry peer group for the two-year performance period. The fair value of each performance share unit award is estimated using a Monte Carlo simulation model that uses various assumptions, including an expected volatility rate and a risk-free interest rate. For the year ended December 31, 2022, the weighted-average expected volatility rate was 37.9% and the weighted average risk-free interest rate was 1.43%. For the performance share unit awards granted during the year ended December 31, 2022, the number of shares earned varies based upon the Company achieving certain performance criteria over a two-year performance period. No performance share unit awards of this type were granted during the year ended December 31, 2023.

A summary of the status of our nonvested shares as of December 31, 2023 and changes during the year then ended is presented below:

As of December 31, 2023, there was $31 million of total unrecognized compensation cost related to nonvested share compensation arrangements granted under the Stock Incentive Plan and the Prior Plan. That cost is expected to be recognized over a weighted-average period of approximately 1.8 years. The value of share awards that vested during the years ended December 31, 2023, 2022 and 2021 was $28 million, $31 million and $18 million, respectively.