The national average U.S. retail price of diesel fuel fell from the previous average of $1.761 to $1.746, the Department of Energy reported May 31.

Once again, the highest prices in the nation were in California, where the average cost is $2.186.

Among the higher prices were New England, at $1.815; $1.940 in the Rocky Mountain region; the Central Atlantic region, at $1.800; and on the West Coast, where the average price is $2.105.

Other prices include the Lower Atlantic region, where the average price is $1.655; the Midwest, at $1.684; the Gulf Coast, at $1.661; and the East Coast, at $1.705.

This seemingly hopeful trend may not last.

That’s because oil prices rose sharply in early trading June 1 to nearly $42 a barrel in the wake of a weekend attack in Saudi Arabia by Islamic militants that left 22 people dead and heightened fears about political instability.

Traders fear the attack could be the start of a concerted al Qaida offensive to disrupt Saudi supplies at a time when oil prices are already high enough to threaten world economic growth, news reports said.

Meanwhile, OPEC ministers are to meet June 3 in Beirut, where they are expected to agree to a rise in crude supply limits of up to 2.5 million barrels per day.

Indonesian Oil Minister Purnomo Yusgiantoro, who is also OPEC president, said June 1 that he wanted a significant rise in production to deflate prices, Reuters news service reported.