Average U.S. gas prices grow 55 cents since January.

The national average price of gas is $2.58 per gallon, as of April 30, marking the highest average so far this year, AAA reported.

Pump prices have soared 55 cents higher since a low of $2.03 in late January, making this the largest seasonal increase in gas prices since 2012. Today’s national average price of gas is the most expensive it has been since Dec. 12, 2014.

Why are prices on the rise? AAA noted the reasons behind the uptick. First, it is common for gas prices to rise in late winter and early spring as refineries conduct seasonal maintenance, which can limit gasoline production. Second, the cost of crude oil has increased by more than $15 per barrel since reaching a six-year low in the middle of March, as the market considers a possible slowdown in domestic oil production. According to AAA, the reduction in growth might mean the market is rebalancing supply and demand in response to relatively low prices this year. Continued conflict, in places such as Yemen and Iraq, also add increased risk and uncertainty, which can lead to higher prices as well.

Gas prices on the West Coast continue to be the highest in the nation due to regional refinery problems and relatively tight fuel supplies. California’s average—which currently stands at $3.53—has been the most expensive in the country since Feb. 26, according to AAA data. Meanwhile, South Carolina offers the lowest average price at $2.31, followed by Oklahoma and Missouri, which both have an average gas price of $2.34.