Although gasoline prices have fallen over the last few weeks, truck drivers, construction companies, farmers and other diesel drivers are well aware that diesel prices have not followed suit, The News-Times (Danbury, Conn.) reports. The U.S. Energy Information Administration this week reported average diesel prices were nearly $2.97 per gallon nationally, compared to $2.72 for gasoline. Ron Planting, an economist with the American Petroleum Institute, said it is difficult for diesel drivers to alter their driving habits. Often they're delivering products to companies and can't cancel trips. By June 1, all refiners were required to switch to a lower-sulfur diesel fuel, because of new Environmental Protection Agency rules. Retailers must switch to the lower-sulfur product by Oct. 15, according to The News-Times. Preparing for the switch likely contributed to higher diesel costs, said Michael Burdette, a senior analyst with the EIA. The higher price also can be attributed to a growing demand for heating oil as the weather turns cold. Refiners are increasingly producing heating oil, Burdette said, leaving less room for diesel fuel production. With farmers readying for fall harvest, the demand for diesel fuel continues to grow. Still, Burdette said relief could be on the way. Falling crude oil prices could pull diesel prices down, as about half of diesel fuel costs come from crude oil prices. Nationally, diesel prices fell six cents since last week, compared to nearly 12 cents for gasoline, and Burdette predicts prices to drop by 10 to 20 cents in coming weeks.