National on-highway diesel prices were up 2.6 cents from last week, continuing a recent climb.

On Monday, national prices averaged $3.949, $1.03 more expensive than the same time last year, according to the weekly report from the Department of Energy.

The West Coast had the highest gain of 3.3 cents to reach $4.038. All regions gained. California remained the most expensive at $4.145, and the Gulf Coast the cheapest at $3.913.

Crude oil rose several days last week, but fell on Monday after President Obama and Congress failed, again, to reach a deal on the U.S. debt ceiling. Crude for September delivery dropped 67 cents, or 0.7%, to settle at $99.20 a barrel on the New York Mercantile Exchange. Prices have increased 26% in the past year.

Markets are getting jittery in the face of the debt limit deadlock. Credit rating agency Standard & Poor has warned that the U.S. credit rating has a 50% chance being downgraded from AAA to AA+, which many believe would be catastrophic. The agency also said in a statement that it may lower the credit rating even if a deal is reached, if it isn't accompanied by a "credible solution."