CoStar Group (NASDAQ:CSGP) announced today it has commenced a public offering of 3.75 million shares of its common stock, with underwriters granted a 30-day option to purchase up to an additional 562,500 shares.CoStar expects to use the net proceeds of the public offering to fund a portion of the cash consideration in its pending $860 million acquisition of LoopNet Inc. (NASDAQ:LOOP).The transaction will combine two marketing and information service providers to the commercial real estate market, and is expected to close by the end of the year. The company will combine Loopnet’s 4 million registered members with the software products offered by CoStar that allow clients access to its database of over 140,000 buildings.JP Morgan (NYSE:JPM) is the sole book-running manager, with Needham & Company, LLC, Stephens Inc., William Blair & Company, L.L.C. and JMP Securities (NYSE:JMP) acting as co-managers for the offering.