The national average price for diesel fell another 3.3 cents in the week ending May 23, according to the U.S. Department of Energy, but experts say the price drops could be short lived as oil prices are already rising ahead of Memorial Day weekend.

According to the Energy Information Administration, the national average price for diesel was $2.156 for the week. Though it is a drop, it is still nearly 40 cents higher than the same time period in 2004.

California posted the highest prices, but even that region saw a drop of 5.9 cents, down to $2.373 per gallon. The rest of the West Coast, meanwhile, fell 5.8 cents to $2.339 per gallon.

The biggest drop came from the Rocky Mountain region, where prices fell 6 cents to $2.207 per gallon.

The East Coast averaged $2.181 per gallon, even though two of its three regions were much higher than that. New England posted an average of $2.338 per gallon, while the Central Atlantic states came in at $2.292 per gallon. The Lower Atlantic states balanced out the region at an average of $2.119 per gallon.

Meanwhile, the Midwest posted an average of $2.097 per gallon, while the Gulf Coast came in at $2.112 per gallon.

But those price drops aren’t expected to last as Memorial Day nears – and the summer driving season along with it.

Already prices for light, sweet crude oil have begun to rise from their low points during the previous week. In trading on the New York Mercantile Exchange, the oil was going for $49 a barrel.

While that’s lower than the record highs in the low 50s of a few weeks ago, it’s up from $46 a barrel just a few days ago.