In an effort to combat high gasoline prices in California, billionaire environmentalist activist Tom Steyer is pushing for a state ballot measure to pass an oil severance tax.

Steyer, founder of NextGen Climate, announced support for the potential ballot measure earlier this month at the California Democratic Party convention.

“I want to understand why Californians are paying up to $1 billion more to oil companies per month for gasoline prices than anywhere else in the country,” Steyer said.

California has the highest gasoline prices in the nation, where a gallon of regular gasoline is $3.739, a dollar more than the national average.

According to the Los Angeles Times, one measure would impose a 10 percent oil extraction tax, while the other would “strengthen disclosure requirements for oil companies’ management of gasoline supplies and prices.”

In a letter to the California lawmakers, Steyer, along with Jamie Court—president of Consumer Watchdog—blamed the oil industry for a lack of transparency over prices and inventory levels.

“The oil industry must answer for this half-billion dollar cost to Californians,” they wrote. “The market is rigged to the benefit of an oligopoly and the rules need to be changed to benefit consumers rather than the oil industry.”

Nick Loris, senior policy analyst at The Heritage Foundation, believes that high costs of energy in California are directly related to state policy and taxes.

“The economic and regulatory environment in California is a big reason the costs of energy are so high in California,” Loris said. “If Californians want lower prices, they should urge their politicians not to implement higher taxes to fund their pet projects, especially since those projects tend to be economic disasters.”

In 2006, the California State Legislature passed the California Global Warming Solutions Act, requiring a statewide reduction in greenhouse gas emissions.

This legislation created a cap-and-trade program, requiring oil refiners to purchase pollution credits from the state.

Tupper Hull, spokesman for the Western States Petroleum Association, believes that an emphasis on market-based programs will provide the lowest costs to the consumer.

“We have an opportunity to have a conversation about state regulations,” Hull told The Daily Signal.

Hull argues that proponents of the tax contradict themselves when they call for lower energy prices but seek to increase the cost of raw materials through a severance tax.

“Simplifying and reducing the number of contradictory kinds of program would allow for a lower cost and more efficient means of complying with climate change initiatives,” Hull said.

This isn’t the first time California has considered an oil extraction severance tax.

In 2014, a bill authored by California state Sen. Noreen Evans would have established an oil and gas production tax. The bill failed to make it out of committee.