A trader bought 50,000 September $5.5 calls at $0.22 and sold 100,000 September $6 calls at $0.12 for a credit of $0.02 or $100,000.
As you can see from the risk/reward graph above, the front spread has unlimited risk to the upside and limited profit potential. The unlimited risk is caused by being naked short the higher strike calls. The max gain would occur at an underlying price of $6. At an underlying price of $6, the short calls would expire worthless, and our long calls would be intrinsically worth $0.50 per contract.
The daily chart above shows C dating back to March 2009. At September expiration, the spread would be profitable for any underlying price below $6.52. The 52-week range for C is a low of $3.15 and a high of $5.15.
It's interesting to note that hedge fund manager, David Tepper, raised his Citigroup Inc. stake by 73% in the fourth quarter. Tepper's Appaloosa Management LP's holdings in Citigroup rose to 138.1 million common shares at December 31 from 79.7 million shares at September 30, according to a Form 3F filed with the U.S. Securities and Exchange Commission. Appaloosa also increased their stake in Bank of America, Wells Fargo, and JPMorgan Chase.
A September $5/$5.5 front spread 18,000x36,000 for a credit of $0.03 also traded today.