U.S. gasoline prices (search) fell for the third week in a row as the latest pump price dropped a slight 0.4 cent over the last week to $1.846 a gallon, the government said Monday.

The national average price for regular unleaded gasoline is 15 cents higher from a year ago but at the lowest level since early May, according to the Energy Information Administration's (search) weekly survey of service stations.

Pump prices usually fall in September after the busy summer driving season comes to an end.

The report also showed the retail price for cleaner-burning reformulated gasoline, sold in polluted metropolitan areas, declined 0.9 cent to $1.915 a gallon.

The West Coast had the most expensive regular unleaded gasoline, with the price down 1.6 cents to $2.025 a gallon. San Francisco topped the agency's city survey of gasoline costs, with the price down 1.8 cents to $2.087 a gallon.

The U.S. Gulf Coast (search) had the cheapest fuel, with the price down a penny to $1.744 per gallon. Houston had the least expensive gas as the price fell 1.7 cents to $1.709 a gallon.

The weekly report also showed gasoline prices were down 0.3 cent to $1.982 in Seattle, down 0.6 cent to $1.924 in Miami, down 1.2 cents to $1.912 in New York City, up 1.8 cents to $1.886 in Chicago and up 1.6 cents to $1.816 in Cleveland.

Separately, the EIA survey said the average pump price for diesel fuel increased half a penny to $1.874 a gallon, up 40 cents from a year earlier.

Truckers on the West Coast paid the most for diesel fuel at $2.04 a gallon, up a slight 0.2 cent from the prior week. The Gulf Coast states had the cheapest diesel at $1.826, up 0.7 cent.