Average retail pump prices for diesel and gasoline dropped slightly this week, according to data tracked by the Energy Information Administration (EIA).

The national average for diesel fuel dropped 4/10ths of a penny to $3.879 per gallon, EIA reported, which is 11.2 cents per gallon cheaper compared to the same week in 2012.

The agency said diesel increased in four U.S. regions while dropping in the other five, with increases occurring in: California (up a penny to $4.066 per gallon); New England (up 2.6 cents to $4.006); the Central Atlantic area (up 2.3 cents to $3.972); and the East Coast as a whole (up 6/10ths of a penny to $3.912).

The West Coast witnessed the biggest one-week drop in average retail pump prices for diesel according to EIA – a 2.3 cent drop to $3.906 per gallon – with the Lower Atlantic region home to the second biggest weekly decline at 1.1 cents to $3.837.

The national average for gasoline slid 3/10ths of a penny to $3.269 per gallon this week, the agency noted; a price 8 cents per gallon cheaper compared to the same week in 2012.

Gasoline prices increased in four regions of the U.S. while dropping in the other five, EIA said. Prices increased in New England (up 1.9 cents to $3.494 per gallon), the Midwest (up 1.1 cents to $3.132), the Central Atlantic area (up 6/10ths of a penny to $3.447), and the West Coast (up 2/10ths of a penny to $3.477).

The agency pointed out, though, that if California is removed from the mix, average gasoline prices along the West Coast actually declined 2/10ths of a penny to $3.298 per gallon.

EIA said the biggest one-week decline in average gasoline prices occurred in the Rocky Mountains – a 3.6 cents drop to $3.077 per gallon, which is also the cheapest price for gasoline in the country this week – followed by a 2.5 cent drop in the Lower Atlantic region to $3.30 per gallon.