Standard & Poor’s Goldman Sachs Commodity Index (S&P GSCI) is the largest tradable commodity index fund in the world with more than $80 billion in S&P GSCI-related investments. Investors have been led to believe that investing in the S&P GSCI during periods of rising commodity prices will be profitable. However, the return performance of the S&P GSCI rarely equals the price change of its underlying spot commodities over the long run. This paper examines the historical excess returns of S&P GSCI futures holdings from 2007 to 2013, duplicating the official S&P GSCI trading methods, and finds that S&P GSCI excess returns differ from returns on corresponding investments in commodity futures due to the interaction between term structure effects and futures returns.