U.S. diesel prices are up again this week by less than a tenth of a cent to $3.856, while the nation's gas prices are up by a little more than 4 cents to $3.482, according to the U.S. Department of Energy's weekly report.

Both diesel and gas prices have been slowly creeping upward for the last month and a half, with the last price decrease taking place in mid-December, according to figures from the DOE's Energy Information Administration. The current diesel price is up 34 cents from a year ago, and gas prices are up 35 cents this week from 2011.

On Monday, U.S. oil futures fell below $97 a barrel, the same day new sanctions were announced against the world's third-largest exporter, Iran. The sanctions are supposed to make it harder for Iran to sell its oil through traditional banking routes. The idea is to force Iran to sell its oil at a discount, and reduce the oil revenue Iran uses to run its economy and fund its nuclear operations.

Abundant U.S. oil supplies kept prices in check despite the new sanctions against Iran. Crude supplies are expected to keep growing into spring as the petroleum industry ramps up drilling projects.

Brent crude prices rose to $1.35 to finish at $115.93 a barrel in London. The increase is due to winter storms that brought icy temperatures to much of Europe.