v3.25.3
STOCK-BASED COMPENSATION (Tables)
 9 Months Ended
Sep. 30, 2025
Share-Based Payment Arrangement [Abstract]  
Stock-based compensation expense Stock-based compensation expense was as follows:
 Three Months Ended September 30,Nine Months Ended September 30,
 2025202420252024
Stock Compensation Expense($ in millions)
Stock-based compensation$6.3 $6.3 $20.8 $17.3 
Mark-to-market adjustments2.3 0.3 (3.4)(2.9)
Total expense$8.6 $6.6 $17.4 $14.4 
Schedule of fair value of performance share awards granted valuation assumptions The fair value of each performance share award based on TSR was estimated on the date of grant, using a Monte Carlo simulation model with the following weighted average assumptions:
Grant Date Assumptions - Performance Shares20252024
Risk-free interest rate4.27 %4.53 %
Expected volatility of Olin common stock37 %41 %
Expected average volatility of peer companies35 %37 %
Average correlation coefficient of peer companies0.450.40
Expected life (years)3.03.0
Grant date fair value (TSR-based award)$27.46$72.80
Grant date fair value (net income-based award)$27.62$54.07
Performance share awards granted573,479180,714