The national average for on-highway diesel fuel fell 1.2 cents to $3.937 last week after several weeks of steady climbing.

Prices fell in seven of ten regions defined by the Energy Information Administration. The West Coast saw the largest drop at 3.8 cents, averaging $4.00 per gallon even. The Gulf Coast dropped by nine-tenths of cent an remained the cheapest region at $3.904.

New England had the highest rise by eight-tenths of cent, landing at $4.045. The Rocky Mountain region rose by seven-tenths to $3.855, and the Central Atlantic remained unchanged at $4.09.

Crude oil fell in a market reversal on Monday. Light, sweet crude for September was down 81 cents, or 0.9%, at $94.89 a barrel on the New York Mercantile Exchange.

Markets reacted positively early in the day after an agreement was announced between President Obama and Congressional leaders to raise the debt ceiling. However, the momentum was unsustainable in the face of a poor economic outlook.

Weak manufacturing, and accompanying fears of an economic slowdown, likely caused the market downturn. The Institute for Supply Management said its manufacturing purchasing managers' index fell to 50.9 in July from 55.3 in June. Readings above 50 indicate expanding activity, and the report was well short of economists' expectations for a reading of 54.6.