NEW YORK—Commodities extended their slide Wednesday as crude oil fell below $125 a barrel, dragging down gold, soybeans, wheat and other hard assets as traders shifted money into equities.

Crude dropped about $4 a barrel, bring total losses from the last seven trading days to more than $20 a barrel, or 14 percent. The steep decline has weighed on other commodities and raised questions about whether the bull-run in futures markets may be slowing down as a global economic slowdown cuts into demand for energy and raw materials.

Precious metals posted some of the day’s most...