The pump price of on-highway diesel continued to slide last week, dropping 8 cents nationally to $3.940 per gallon.

New England and the West Coast saw steep drops of 16 and 15 cents respectively, landing at $4.105 and $4.146. The Gulf Coast maintained the lowest price at $3.877; California the highest at $4.223. Diesel is still nearly one dollar more expensive than this time last year.

Crude oil is also falling. On Monday, light, sweet crude for July delivery dropped back below the $100 mark to end at $99.01, the lowest close since May 23.

Last week's disappointing U.S. economic data on both manufacturing and jobs prompted a tepid start to the week for most assets and renewed questions about global energy demand. Worries about the economies of Europe and Japan also impacted price.

This Wednesday in Vienna, the Organization of Petroleum Exporting Countries will meet for the first time since turmoil broke out in the Middle East to decide production levels.

The organization has not changed output levels since December 2008, when it cut output to put a floor on falling prices at the beginning of the recession. As prices have jumped by more than 35 percent since last year, many analysts think OPEC will once again increase production, and hence lower global prices.