iShares S&P GSCI Commodity-Indexed (ETF) (GSG)

The ETF seeks to track the performance of the GSCI Excess Return Index. The fund will invest in a portfolio of exchange-traded futures contracts tracked by the index. The index currently tracks 24 different commodities. It is weighted with approximately 67% invested in energy, 16% in agriculture, 7% in industrial metals, 7% in livestock and 3% in precious metals. The index is production weighted to reflect the relative significance of those commodities to the world economy.
This ETF differs from GCC in that it is heavily weighted in energy, whereas GCC is a fund that is equally weighted across commodity categories. That said, I expect this fund to outperform the S&P over the next five years based on my general thesis that we are still in a commodities bear market and prices for all commodities - energy, metals, and agriculture - will increase over time and might be helped along by a fair dose of inflation.

Supply and Demand - Due to the nature of commodities, supply will always decrease. Due to the world population growth, demand will always increase.