Goldman roll
The Goldman roll is the monthly sale and purchase of commodities for the Goldman Sachs Commodity Index (S&P-GSCI).
While a stock market index is a purely mathematical construct, a commodity index requires entering a long position or ownership of a physical product through a futures exchange. These contracts must be released and renewed, typically monthly. This roll yield both creates and requires arbitrage opportunities which are statististically significant, measuring a Sharpe ratio as high as 4.4 between 2000 and 2010.