Commodities prices suffered their largest monthly drop in 28 years in July as crude oil prices nose-dived more than $20 from an all-time high of $147.27 a barrel.

The Jefferies-Reuters CRB index, a global commodities benchmark, lost 10 per cent, its largest monthly decline since it fell 10.5 per cent in March 1980, amid worries about lower economic growth damping demand for raw materials.