Commodities on Wednesday posted the biggest gain in almost four weeks, led by industrial metals and energy, on speculation that more economic stimulus in the U.S. and low interest rates will bolster demand for raw materials.

The Standard & Poor’s GSCI Index of 24 raw materials rose 2.1 percent to close at 671.99 at 3:46 p.m. New York time, the biggest gain since Aug. 11. Nickel jumped 5.3 percent, the most since May 2010, and crude oil gained as much as 5.2 percent. The commodity gauge fell in the previous three sessions on concern that Europe’s debt crisis will hinder the global economy.

“Although growth prospects remain bleak, the market is looking past current weakness in anticipation of further stimulus out of the U.S. and anticipation that the Chinese may resume their pro-growth policies,” Scott Gardner, the chief investment officer at Verdmont Capital SA in Panama, said in an e-mail. He helps manage $450 million in client assets.

President Barack Obama will unveil his proposal for promoting job growth tomorrow in an address to a joint session of Congress. The plan includes the injection of more than $300 billion into the economy next year, mostly through tax cuts, infrastructure spending and direct aid to state and local governments.

Oil, Copper

Crude-oil futures topped $90 a barrel in New York as a weather system threatened to reduce U.S. production from the Gulf of Mexico.

Copper futures climbed 1.9 percent in New York as strike threats at mines in Peru and Indonesia heightened concern that a projected global shortfall will increase. Gold futures dropped the most in two weeks.

“The market is following the ‘risk-on’ pattern,” Stanley Crouch, who helps oversee $2 billion as the chief investment officer of Aegis Capital Corp. in New York, said in an e-mail. “Gold, on the other hand, is the obvious loser from the risk-on trade.”

The MSCI All-Country World Index of shares rose as much as 2.8 percent. The Standard & Poor’s 500 Index gained 2.9 percent, snapping a three-session decline.