Washington gasoline prices have surpassed those of California to become the most expensive in the country as drivers there bear the brunt of the state’s effort to cut carbon emissions.

Gasoline prices in Washington have risen to $4.98 a gallon, according to data from auto club AAA. Until this summer, Washington prices have been below California for more than nine years.

Washington limits carbon emissions from power plants, refineries and other high-emitters by requiring companies to buy credits for greenhouse gases. These credits have soared to 53 cents a gallon, a 55% jump since the program, known as cap-and-invest, began this year, according to data from Opis.

Carbon credits in California, the state with the longest-running carbon capping program, cost just over 11 cents a gallon currently, Opis data show.

Washington’s carbon credits are unlikely to get cheaper any time soon given the aggressive targets the state set, according to Jim Mladenik, senior associate at consultancy Stillwater Associates.

Read more: Following California, Washington Starts Cap and Trade Market (3)