Another thought:are you choosing between commodities (oil,gas,gold,...)choosing between contracts for a given commodity (WTI, Brent, Dubai, ...)choosing between maturities for a given commodity contract (Feb 2010, Mar 2010, ...)According to academics I know, most of commodity liquidity is in futures, much less in options. But I'm not (yet) a practisioner.I think you'll find WTI and Brent crude oil, nearest and 2nd nearest months futures are the most liquid commodity contracts in the world. Greatest liquidity falls away from 1st month to 2nd month in a fairly predictable manner before maturity for a given commodity, as people roll.You also get spots of liquidity further along the WTI futures curve in the December contracts, see for WTI
http://www.cmegroup.com/trading/energy/ ... tures.html and look at the open interest.Good idea on the commodity index compositions. But I think their major weighting is "composition of world trade" or similar.