Diesel prices across the nation continued their upward trend, gaining half a penny this week to a national average of $3.074 a gallon

, according to weekly figures released by the U.S. Energy Information Administration.

Two weeks ago, diesel had topped $3 a gallon for the first time since November 2008. This week, trucking's main fuel was over $3 a gallon in every region. The national average was 85.3 cents higher than the same week last year. The West Coast had the highest prices, averaging $3.203 a gallon, while the Lower Atlantic had the lowest at $3.033 a gallon.

In an analysis sent out last week, Charles W. Clowdis, Jr., managing director of transportation consulting for IHS Global Insight, said motor carriers will be impacted most strongly by the increases in diesel prices this summer. Higher diesel prices will result in greater fuel surcharges that will be passed on to the shipper, he said. Rising fuel costs will also impact owner-operators, who are least able to pass along higher fuel costs, he added.

"Overall, the diesel fuel price increase coming this summer can have an adverse impact on the carrier segment already experiencing lowered capacity, resulting in job losses and disruptions to the supply chain," Clowdis said.

While diesel prices continued to inch up, crude oil prices fell Monday as concerns over the Goldman Sachs fraud charges continued and new worries sprouted over the Icelandic volcano, according to the Associated Press.

On Friday, the Securities and Exchange Commission announced it was charging investment bank Goldman Sachs with fraud related to subprime mortgages. The news sent commodity and stock prices down, as worried investors ditched risky assets.

Those worries were compounded Monday, as the Icelandic volcano had investors concerned that the disruption in air travel would lower demand for jet fuel.

After falling $2.27 a barrel Friday, crude dropped $1.84, or 2.2 percent, Monday to $81.40 a barrel on the New York Mercantile Exchange, the AP reports.