By David Russell, reporter at OptionMonsterNEW YORK -- The bulls are rolling the dice on Macau casino operator Melco Crown Entertainment ( MPEL). OptionMonster's tracking systems detected the purchase of about 6,000 June 11 calls for $1.70 to $1.75 Tuesday. Volume was more than 100 times open interest in the strike, indicating that this was new activity. Calls lock in the price investors must pay to buy stock, so they can generate significant leverage if it appreciates. But they will also lose value if a rally doesn't materialize. Melco shares declined 2.4% to $12.19 Tuesday. The stock almost doubled between December and late April but has pulled back sharply since then. The shares are now attempting to hold above their 200-day moving average, around the same level where they peaked in late October and early November. That could be leading some chart-watchers to believe that they're at support and now due for a rebound. Overall option volume was twice the average amount Tuesday, and calls outnumbered puts by a bullish 11-to-1 ratio. Russell has no positions in MPEL.