Falling oil prices will be a boon to consumers who can expect to pay less for food, Citigroup's Aakash Doshi said in a Dec 3 report. About 45 percent of the operating expenses of growing and harvesting rice comes from inputs such as fuels, lubricants, electricity and fertilizer, according to a US Energy Information Administration analysis of US Department of Agriculture data.

Energy accounts for about 54 percent of costs of corn and wheat.

Energy makes up 30 to 40 percent of operating costs for mining, according to Citigroup. The bank estimates that a further 20 percent drop for oil, along with gains for the dollar, would cut thermal coal costs by 13 percent and iron ore by about 6 percent.

Cereal maker Kellogg Co expects "relatively benign" commodity inflation, Chief Financial Officer Ronald Dissinger said on Oct 30. The slump in oil will make some cotton fabric cheaper, Bryan Timm, chief operating officer of Columbia Sportswear Co, said on an Oct 30 conference call.

Not all commodities will benefit from cheaper oil. While energy accounts for about 40 percent of the cost of making aluminum, most of that fuel is coal or hydro-electric power, which have little or no relationship with crude prices, Haigh said in a report last month.

This year's oil slump may have come too late to benefit US farmers.

Growers usually buy tractor diesel, energy-based fertilizers and pesticides well before the harvests, which started in September for the biggest crops, corn and soybeans.

That means prices will need to remain lower for months to reduce farming costs for next season, Michael Swanson, a senior agricultural economist at Wells Fargo Co, the biggest US farm lender, said last month.

What is happening in oil might be separate from other commodities, said David Rosenberg, the chief economist at Gluskin Sheff & Associates Inc in Toronto.

Crude is dropping because of too much supply, not because demand is weak, so better economic growth should mean buoyant consumption for other raw materials, he said.

OPEC last month kept its output target unchanged even after the steepest slump in oil prices since the global recession.