.93 , $ 24.98 and $ 15.32 , respectively . the fair value of the espp offerings is estimated on the offering period commencement date using a black-scholes pricing model with the expense recognized over the expected life , which is the six month offering period over which employees accumulate payroll deductions to purchase the company 2019s class a common stock . the weighted average fair value for the espp shares purchased during 2007 , 2006 and 2005 were $ 9.09 , $ 6.79 and $ 5.15 , respectively