By David Russell, reporter at OptionMonsterNEW YORK -- The bulls have been targeting Staples ( SPLS) recently, and Wednesday they were back in the trade. OptionMonster's tracking programs detected the purchase of about 33,000 September 15 calls for 70 cents to 80 cents. Volume was almost 155 times previous open interest at the strike, indicating that new money was put to work. Calls lock in the price where investors can buy shares in the office-supply retailer. That can result in some nice leverage in the event of a continued rally, but they can become worthless if it doesn't move. Shares of Staples fell 1.32% to $13.48 Wednesday but are up more than 20% in the last month. The stock bottomed around $11 in August, its lowest price since early 2003. Other office retailers have been gaining as well, making them the third-best performing group on OptionMonster's propriety researchLAB service in the same period. Total option volume was more than six times greater than average in the session, with calls outnumbering puts by a bullish 65 to 1. Russell has no positions in SPLS.