The Supreme Court declined to review whether the US Environmental Protection Agency acted appropriately in rejecting Oklahoma's plan to address visibility at national parks and wildlife areas.

Last July, the 10th Circuit Court ruled that the EPA lawfully exercised its authority to reject Oklahoma's state plan and instead impose a federally authorised plan on the state.

OG&E and Pruitt launched an appeal this January.

“We still believe that the Oklahoma state implementation plan would have enabled us to meet the regional haze requirements at a much lower cost.

“However, we accept the court's ruling and now turn our attention to meeting the 55-month compliance deadline,” OG&E spokesman Paul Renfrow said.

OG&E estimated the cost of complying with the EPA’s ruling at $US1 billion ($A1.07 billion).

Oklahoma officials maintain that a state-run policy would be just as effective but more cost-efficient.

OG&E said the Oklahoma plan had called for use of low-sulphur coal and would have given affected state utilities the flexibility of achieving the visibility improvement goals of the regional haze rule in a more cost-effective way.