The price of on-highway diesel dropped significantly again last week, although not quite as steeply as the previous week.

Nationally, prices came down 3.8 cents to $3.85 per gallon. California diesel continued to sink fast with an 8.1 cent fall after a nine cent drop the week before. But at $4.065, it remained the most expensive. The Gulf Coast region was the cheapest at $3.798.

Prices are still up 92.6 cents nationally from one year ago.

Crude oil, on the other hand, climbed to a three-week high on signs of economic growth in the U.S. and China, the world's two biggest oil consumers. Crude for August delivery gained $1.95 to $96.89 a barrel on the New York Mercantile Exchange, the highest settlement price since June 14.

Carl Larry, director of energy derivatives and research with Blue Ocean Brokerage LLC in New York, told Bloomberg oil may rise to $100 this month.

The price spike comes despite an effort by the International Energy Agency along with the Obama administration to release emergency oil onto world markets.