By David Russell, reporter at OptionMonsterNEW YORK -- Traders want to generate some profits with electricity producer Calpine ( CPN). OptionMonster's tracking programs detected the purchase of some 1,600 June 21 calls for 55 cents to 70 cents. Volume was more than 10 times previous open interest at the strike, indicating that new positions were initiated. These calls lock in the price where shares can be purchased, letting investors cheaply position for a rally before the end of the week. The contracts can also generate significant leverage, doubling or tripling from even a small gain in the underlying stock. Calpine rose 1.97% to $21.73 on Friday and has been slowly trending higher since the market bottomed more than four years ago. It began the month around $19.50, rallied above its 50-day moving average, consolidated, and is now continuing to the upside. Total option volume was seven times greater than average in the session, with calls outnumbering puts by a bullish 21-to-1 ratio. Russell has no positions in CPN.