U.S. oil prices fell Monday on renewed concerns that the OPEC cartel's recent cut in production would not be enough to counter the impact of a global economic slowdown. U.S. light sweet crude for September delivery traded down 1.4 percent, or 23 cents, at $26.96 a barrel. London Brent futures for September delivery traded down 21 cents to $24.98 a barrel. Oil prices have declined steadily since late May amid increasing evidence that the global economic slowdown is eating into demand for petroleum this year. Concern over falling prices and a sustained rise in spare petroleum stocks spurred the OPEC producer cartel to agree last week to a 1 million barrels per day (bpd) output cut. But traders were reluctant to push prices up without indications that the world economy is rebounding.