The national average price for diesel fell for the fourth straight week for the week ending Sept. 11, says the U.S. Energy Info Administration (EIA). The national average was $2.857, down from $2.967 the previous week.

Meanwhile, gasoline prices continue to plummet, with the national average for regular falling almost 11¢ from the previous week's average to $2.618/gal. on Sept. 11, EIA reports.

Mike O'Connor, president of the Virginia Petroleum, Convenience and Grocery Association (VPCGA), says in a Sept. 12, USA Today article that gasoline prices are plummeting because “they shouldn't have been that high in the first place. Two reasons they were: fear and speculation.” VPCGA represents gasoline distributors who operate about 4,000 stations.

What's more, O'Connor says $2 gasoline “is more likely than unlikely” if the Gulf of Mexico isn't hit by hurricanes and theres no flare-up of tensions in oil-producing regions.