Oil industry economists say a link between ending a 40-year oil export ban and lower prices at the gas pump is not as direct as Republican presidential candidate Jeb Bush would have voters believe in his new energy proposal.

Bush’s overall premise that lifting the ban would expand economic growth holds up to independent scrutiny. However, environmentalists say the negative impact on the planet would be too great.

Eliminating the export ban, enacted in the 1970s, is the key piece of Bush’s proposal, first published in a paper online Tuesday. Bush cites studies suggesting a drop of 6 cents per gallon over time if the ban were lifted.

Many economists note that oil is a global commodity and say U.S. production has little to do with overall pricing.