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The average retail price of U.S. diesel fuel dropped for the 10th consecutive week, the Department of Energy reported, but the gap between diesel and gasoline price reached the widest spread since the agency began publishing diesel prices in 1994.

President-elect Barack Obama has chosen the Nobel-prize-winning head of a California research institute and a former New Jersey environmental official to fill his cabinet positions heading the Department of Energy and the Environmental Protection Agency, Bloomberg reported Thursday.

California regulators are considering a first-in-the-nation plan that would require almost all privately owned heavy-duty trucks in the state to install particulate filters to reduce soot emissions by 85%, the San Jose Mercury News reported Thursday.

A Navistar Inc. spokesman said that a “coalition is building” around the company’s call to the incoming Obama administration to ease 2010 emissions mandates, but the Environmental Protection Agency said its tightened standards would go into effect without delays.

Volvo AB and Daimler AG are producing global heavy-duty engine platforms for use in North America, Europe and Asia, and other manufacturers plan to introduce their own versions, pushed by converging emission regulations, the need to reduce research and development costs and to take advantage of economies of scale, according to industry analysts and executives.

Diesel fuel prices continued to slide last week, with the U.S. average falling 4.9 cents to $2.615 a gallon, according to the Department of Energy.

Truck and engine maker Navistar Inc. said it will take a “leadership role” in trying to convince Congress and the new administration to delay full implementation of 2010 heavy-duty truck engine emission mandates.

Clean Energy Fuels Corp. has started up its California LNG Plant in Boron, Calif., the company said Monday.