Activity under our stock option plans, as well as non-plan activity are summarized below (shares in thousands): Our option plans allow for stock options issued as the result of a merger or consolidation of another entity, including the acquisition of minority interest of our subsidiaries, to be added to the maximum number of shares provided for in the plan (Substitute Options). Consequently, Substitute Options are not returned to the shares reserved under the plan when cancelled. During 2001, 2000 and 1999, the number of Substitute Options cancelled were immaterial. Options for 2.4 million and 2.1 million shares were exercisable at December 31, 2000 and 1999, respectively. The options outstand- ing at December 31, 2001 have been segregated into three ranges for additional disclosure as follows (option shares in thousands): In addition, Ingenex has a stock option plan under which options to purchase common stock of Ingenex have been and may be granted. No options had been granted under such plan since 1997. We have elected to follow APB 25 in accounting for our stock options because the alternative fair value method of account- ing prescribed by SFAS 123 requires the use of option valua- tion models that were not developed for use in valuing employee stock options. Under APB 25, no compensation expense is recognized when the exercise price of our stock options equals the market price of the underlying stock on  the date of grant. For the years ended December 31, 2001, 2000 and 1999, compensation costs for options granted to  employees and consultants were $1.1 million, $1.0 million and $0.2 million, respectively. Pro forma net loss and net loss per share information required by SFAS 123 has been determined as if we had accounted  for our employee stock options under the fair value method  of SFAS 123. The fair value for these options was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions for 2001, 2000 and 1999: weighted-average volatility factor of 0.86, 0.90 and 0.80, respectively; no expected dividend payments; weighted- average risk-free interest rates in effect of 3.9%, 5.0% and  6.0%, respectively; and a weighted-average expected life of 2.99, 3.69 and 2.52, respectively. Twenty-Seven Number Weighted- Shares Available of Options Average for Grant Outstanding Exercise Price Balance at December 31, 1998 868 1,924 $ 5.45 Increase in shares reserved 226 — — Options granted (784) 1,597 $ 8.12 Options exercised — (147) $ 3.32 Options cancelled 67 (70) $ 4.84 Balance at December 31, 1999 377 3,304 $ 6.82 Increase in shares reserved 1,500 — — Options granted (748) 748 $ 36.20 Options exercised — (353) $ 4.31 Options cancelled 28 (33) $ 19.17 Balance at December 31, 2000 1,157 3,666 $ 12.95 Increase in shares reserved 1,000 — — Options granted (1,300) 1,300 $ 15.21 Options exercised — (404) $ 3.26 Options cancelled 434 (434) $ 26.35 Balance at December 31, 2001 1,291 4,128 $13.20 Options Outstanding Options Exercisable Weighted-Average Number Remaining Life Weighted-Average Number Weighted-Average Range of Exercise Prices Outstanding (Years) Exercise Price Exercisable Exercise Price $ 0.08–$ 7.50 1,620 5.99 $ 5.30 1,587 $ 5.29 $ 8.39–$12.69 1,646 8.73 $12.01 626 $12.48 $12.75–$46.50 862 8.77 $30.31 375 $30.87 4,128 7.66 $13.20 2,588 $10.73