After reading this article on commodities in The Economist that cited "a recent report by Société Générale" who analyzed 5 commodities booms since 1975. "They lasted 28 months, on average, during which prices rose 35%." While it's not clear whether the 35% refers to an average rise or maximum, that number pales next to the "several-fold" rise claimed by Puru Saxena here (for the Daily Reckoning). And yet, despite the credit I give the former over the latter, the CRB chart supports Saxena more. Note the doubling from '72 to '73. More CRB information here.