By Jud Pyle, CFA, chief investment strategist for the Options News NetworkA bullish investor lit up call activity in Atlanta-based electricity seller Mirant ( MIR) today, a few weeks before the company is scheduled to announce second-quarter earnings figures. The investor sold to close 10,000 July 15 calls for 35 cents and simultaneously bought to open 10,000 Sept. 12.5 calls for $3.05 with the stock trading at $15.07 a share. The July 15 calls are currently trading up 20 cents on the day and are home to current open interest of 11,000 contracts. The Sept. 12.5 calls, which have gained 38 cents so far today, are home to current open interest of just 721 contracts. This strategy is considered a rollout; the investor isn't yet finished with Mirant and is moving his or her soon-to-expire July contracts out to a later-dated series. Normal daily volume in Mirant rarely exceeds 10,000 contracts, but we saw at least one investor's trade double volume across all strikes today. In addition, July 15 and Sept. 12.5 are the only two strikes that have seen significant volume today; the remainder of the strikes have seen little (or no) volume. Mirant stock has rallied more than 60% since reaching a 52-week low of $9.25 on March 6, but these shares are off approximately 14% from a recent high of $17.36. The investor needs Mirant stock to expire higher than $15.55 on September expiration. Mirant shares are currently trading up 54 cents so far today to $15.40.