Exports of LNG from the U.S. will slow as domestic gas demand there grows and available supply there is used up, said ConocoPhillips (NYSE: COP) CEO Ryan Lance at a gas industry conference on April 4 in Chiba, Japan.

"By the mid-2020s, the existing brownfield supply expansion options will be exhausted, both in the U.S. and other countries. New greenfield projects will be needed," Lance said.

"To justify those investments, higher energy prices will be required," he said.

As supplies grow tighter, he added, the industry will also need to return to longer-term contracts that provide security of supply for end users and security of demand for suppliers.