During the six months ended November 30, 2018, we granted non-qualified stock options covering a total of 95,600 common shares under our stock-based compensation plans. The weighted average option price of $42.86 per share was equal to the market price of the underlying common shares at the grant date. The fair value of these stock options, based on the Black-Scholes option-pricing model, calculated at the grant date, was $12.55 per share. The calculated pre-tax stock-based compensation expense for these stock options is $1,200,000 and will be recognized on a straight-line basis over the three-year vesting period, net of any forfeitures. The following assumptions were used to value these stock options:

Dividend yield	2.01% - 2.16%
Expected volatility	33.04% - 33.60%
Risk-free interest rate	2.77% - 2.96%
Expected term (years)		6.0

Expected volatility is based on the historical volatility of our common shares and the risk-free interest rate is based on the U.S. Treasury strip rate for the expected term of the stock options. The expected term was developed using historical exercise experience.

Service-Based Restricted Common Shares

During the six months ended November 30, 2018, we granted an aggregate of 323,925 service-based restricted common shares under our stock-based compensation plans. The fair value of these restricted common shares was equal to the weighted average closing market price of the underlying common shares on the respective dates of grant, or $43.59 per share. The calculated pre-tax stock-based compensation expense for these restricted common shares is $14,119,000 and will be recognized on a straight-line basis over the three-year service-based vesting period, net of any forfeitures.

Market-Based Restricted Common Shares

On September 28, 2018, we granted an aggregate of 225,000 restricted common shares to two key employees under our stock-based compensation plans. Vesting of these restricted common share awards is contingent upon the price of our common shares reaching $65.00 per share and remaining at or above that price for 90 consecutive days during the five-year period following the date of grant and the completion of a five-year service vesting period. The grant-date fair value of these restricted common shares, as determined by a Monte Carlo simulation model, was $23.38 per share. The following assumptions were used to determine the grant-date fair value and the derived service period for these restricted common shares:

Dividend yield	2.16	%
Expected volatility	33.60	%
Risk-free interest rate	2.96	%

The calculated pre-tax stock-based compensation expense for these restricted common shares is $5,261,000 and will be recognized on a straight-line basis over the five-year service vesting period, net of any forfeitures.

Performance Share Awards

We have awarded performance shares to certain key employees under our stock-based compensation plans. These performance shares are earned based on the level of achievement with respect to corporate targets for cumulative corporate economic value added, earnings per share growth and, in the case of business unit executives, business unit operating income targets for the three-year periods ending May 31, 2019, 2020 and 2021. These performance share awards will be paid, to the extent earned, in common shares of the Company in the fiscal quarter following the end of the applicable three-year performance period. The fair values of our performance shares are determined by the closing market prices of the underlying common shares at the respective grant dates of the performance shares and the pre-tax stock-based compensation expense is based on our periodic assessment of the probability of the targets being achieved and our estimate of the number of common shares that will ultimately be issued. During the six months ended November 30, 2018, we granted performance share awards covering an aggregate of 58,200 common shares (at target levels). The calculated pre-tax stock-based compensation expense for these performance shares is $2,494,000 and will be recognized over the three-year performance period as the performance condition is probable.