Deal of the year: Citi

The past 18 months have seen a flurry of deals in which global investment banks retreating from the commodities business have sold books of energy or commodity derivatives. A handful of banks have emerged as the buyers, snapping up the books in an effort to build market share at a time when their erstwhile rivals are pulling out.

Of those banks, Citi has shown the most appetite for other banks' books, buying at least a dozen of them over the past year. In the second and third quarters of 2014