X0304 4 2012-02-21 0001057352 COSTAR GROUP INC CSGP 0001438487 Stanfill John L C/O COSTAR GROUP, INC. 1331 L STREET, NW WASHINGTON DC 20005 0 1 0 0 Sr. VP-Sales, Customer Service Common Stock, par value $0.01 per share 2012-02-21 4 A 0 38800 0 A 89934 D Option to Acquire Common Stock 58.95 2012-02-21 4 A 0 11600 0 A 2022-02-20 Common Stock 11600 11600 D Includes a grant of 8,200 shares of restricted common stock that vest in three equal installments on February 21, 2013, February 21, 2014, and February 21, 2015, and a grant of 30,600 shares of restricted common stock that vest upon CoStar Group, Inc.'s achievement of $90 million of cumulative earnings before interest depreciation and amortization (EBITDA) over a period of four consecutive calendar quarters by March 31, 2017. Represents all shares of common stock owned, consisting of 8,200 shares of Common Stock and 81,734 shares of Common Stock subject to unvested restricted common stock grants. The option vests in three equal installments on February 21, 2013, February 21, 2014, and February 21, 2015. /s/ Jonathan Coleman, Attorney-in-Fact 2012-02-23