Pairs trading is a non-directional strategy that identifies two companies (or futures contracts) with similar characteristics whose price relationship is outside of its historical range. The strategy simply buys one instrument and sells the other in hopes that relationship moves back toward normal. The idea is the price relationship between two related instruments tends to fluctuate around its average in the short term, while remaining stable over the long term.

For example, the price relationship between Bank of America and U.S. Bancorp (BAC/USB) has remained relatively stable at a ratio of 1.5 over the past four years. During that period, its price ratio has been as high as 1.8 and as low as 1.35. The goal is to identify these stable relationships and buy the stock lagging the historical average and sell short the one leading it.