The oil and gas industry substantially rewards US legislators with campaign donations when they oppose environmental protections, according to a new analysis of congressional votes and political contributions.

Oil and gas companies spent $84m on congressional campaigns in 2018. Researchers found a correlation between an increase in anti-environment votes and an increase in contributions. They documented how lawmakers’ scores from the League of Conservation Voters (LCV) dipped and then were followed by campaign funding from the industry.

On average, a 10% decrease in the LCV score in an election cycle was associated with an additional $1,700 in campaign money from the corporations the following cycle.

The peer-reviewed study was published in the Proceedings of the National Academy of Sciences.

The authors also sought to determine whether campaign donations from industry might prompt legislators to vote against environment rules that oil and gas companies saw as a burden. But they concluded there was little or no relationship between campaign contributions in one election cycle and LCV scores in the following period.

“Legislators proved that they’re willing to vote against the environment consistently and then they’re rewarded later,” said co-author Matthew Goldberg, a postdoctoral associate with the Yale Program on Climate Change Communication. “I suppose this is more of an advantage for oil and gas companies because they need to ensure that people are going to vote in their interest.

Goldberg said the findings should encourage people to “get the right people in office, because they’re not as susceptible to money changing their votes”.

The study analyzed data from 1990 to 2018. In 1990, 63% of oil and gas money went to Republicans, Goldberg noted. In 2018, 88% of the industry’s campaign donations were to the conservative party.