U.S. onshore oil production has likely peaked and will start to decline due to the recent plunge in crude prices, jeopardizing the nation’s position as the world’s largest fossil fuel producer and its energy security,

Two big American shale producers said they would cut capital expenditure on Monday in response to sliding oil prices, prompting industry warnings that US production had peaked and could begin falling.

The head of the largest independent oil producer in the Permian Basin predicts US shale production has peaked and will likely decline from here as oil prices hovers near four-year lows. “We have a very good view of what the US looks like.