Diesel fuel prices continue to drop as crude oil futures continue to reflect a worldwide glut. Gasoline prices, however, jumped nearly 30 cents a gallon in California.

Weekly figures released Monday by the U.S. Department of Energy show the national average retail price of a gallon of diesel at $2.814, down 1.8 cents from a week ago and down $1.08 from a year ago.

For regular gasoline, however, the average price was up 4.1 cents per gallon from last week to $2.834. That's still down 80.1 cents from a year ago.

Diesel prices were down in all regions except for the Rocky Mountain region, where they were up 0.2 cents per gallon. The highest diesel prices were in California, at $3.133. The New England and Central Atlantic regions were also over $3 a gallon. The lowest average price was reported in the Midwest at $2.704, followed closely by the Gulf Coast at $2.708.

Gasoline prices were highest on the West Coast at $3.589 per gallon, jumping 29.2 cents from last week.

Drivers in California could see prices top $4 a gallon, reports the Associated Press, noting that a shortage in oil and other components used to make California's unique blend of gasoline.

Even without California, the West Coast saw an average gasoline price of $3.589. The lowest gasoline prices were reported in the Gulf Coast region at $2.527, up 0.8 cents from the previous week.

Negotiations ongoing with Iran over a nuclear deal have been depressing crude oil futures because a deal would mean the country would re-enter an oil market that is already in a glut. U.S. light crude, also known as West Texas Intermediate, closed down 54 cents Monday, or 1%, at $52.20 a barrel, CNBC reports.

Bank of America Merrill Lynch, CNBS reports, said U.S. crude prices "could soon drop well below our $50 per barrel target" for the third quarter of the year.

A weaker dollar also is contributing to lower crude oil futures prices. And the Wall Street Journal reports that news that production has recently increased in Saudi Arabia and North Dakota, despite the global glut, also pushed prices lower. In fact, Saudi Arabia produced a record high output of crude oil in June.