Here’s some good news for President Donald Trump, who’s clearly concerned about the impact of high gas prices on Americans’ wallets (and perhaps their midterm votes): He can slash them without any help from Congress.

Buried within Environmental Protection Agency regulations is a little known premium on every gallon of gasoline and diesel—more than double the federal gasoline tax—and Trump can erase it. If he does nothing, however, that hidden tax is likely to grow.

The culprit is the EPA’s Renewable Fuel Standard, which requires gasoline and diesel producers to blend a certain percentage of biofuels, such as ethanol, into the transportation fuel supply. In March, the EPA raised the quota, finalizing what it proudly called the highest renewable fuel mandate in the program’s 20-year history. The change will increase the amount of biomass-based diesel that is produced by over 60 percent from 2025 levels, according to estimates from the EPA.

The biofuel lobby cheered. But drivers will foot the bill—thanks to the rising price of an accounting mechanism known as Renewable Identification Numbers, or RINs. Fuel refiners use these tradable credits to prove compliance with the EPA’s standards, either by blending gasoline with ethanol themselves or else by purchasing credits on the open market from others, including from foreign suppliers. But either way, as the EPA now concedes, the cost of acquiring RINs gets passed on to gasoline consumers.

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For motorists, that means higher prices at the pump. In fact, the Energy Policy Research Foundation estimates that the cost of purchasing RINs raises the price of fuel by 45 cents per gallon. Given that Americans use 140 billion gallons of gasoline each year, the premium amounts to roughly $63 billion per year transferred from American drivers to the corn- and soybean-oil complex that supplies biofuel.

The problem is that the government’s high biofuel quotas make buying RINs unavoidable for gasoline refiners. Many gas stations, small vehicles and automobiles cannot safely use gasoline that is more than 10 percent ethanol. So to meet biofuel mandates that are now at more than 11 percent, refiners purchase expensive D4 RINs to make up the difference. D4 RIN credits are generated by blending biomass-based diesel, but the EPA allows gasoline refiners to use them to cover their shortfall.

This, in turn, heavily distorts the diesel market. Unlike ethanol, renewable diesel has no “blend wall,” or limit on the amount of the product that can be legally or safely blended into the overall fuel supply. Because of that, biofuel suppliers produce large quantities of renewable diesel just to sell the compliance credits to gasoline refiners. Perversely, the raw material used to make renewable diesel—soybean oil—trades at roughly $2 more per gallon than the fuel does, so biofuel-based diesel suppliers sell the fuel at a loss and rely on exorbitant RIN prices to turn a profit.

A tidier one by the day, as it turns out, since the cost of RINs continues to rise. At the start of this year, D4 RINs traded near $1. In July, the average price was nearly $2.50. Researchers at the University of Illinois project that meeting the new mandate will require D4 RIN generation to rise 55 percent in 2026 and 67 percent in 2027. These would be levels with no precedent in the history of the Renewable Fuel Standard.

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Gasoline refiners are running out of ways to offset the high price. Historically, a modest cushion of unused credits held by refiners has absorbed shocks, but those are being drawn down to meet the new regulations. Bloomberg Intelligence estimates that what’s known as the RIN bank sits at about 1 billion, down from 3.1 billion at the start of the compliance year. As RINs become more scarce, they get more expensive, adding even more to the price Americans pay at the pump. Refiners have no choice but to comply with EPA regulations because violations carry up to a five-figure penalty per day.

Even the EPA understands that the regulations are unmanageable. Refiners keep their compliance costs down by acquiring RINs generated using cheap imported renewable diesel and recycled cooking oil from China, Argentina and Southeast Asia. The EPA proposed a penalty on credits tied to imports but delayed it until 2028—an implicit confession that RINs generated from foreign raw materials are keeping fuel prices from skyrocketing. Regulators, in effect, are taxing American drivers to subsidize Asian cooking-oil exporters.

But fixing this does not require new legislation. Congress handed the EPA full discretion to set biofuel volume requirements after 2022. The president can direct the agency to bring the 2026 and 2027 obligations back to what the market can bear.

Lower gasoline prices are within Trump’s reach. He needs only to tell his EPA administrator, Lee Zeldin, to do what the law already allows.