John Hess, CEO of the Hess Corporation, speaks during the IHS CERAWeek 2015 energy conference in Houston, Texas April 21, 2015. REUTERS/Daniel Kramer

LONDON (Reuters) - The U.S. shale oil industry can maintain flat output if oil prices stay at $50 per barrel, but a price of $60-$80 per barrel is needed to invest in long-cycle projects such as deep-water, the chief executive of oil firm Hess Corp said.

“Because of operational efficiencies and productivity the industry needs $50 (per barrel) to hold shale production flat ... Our company and others have reduced drilling time from rig to rig from 30 days two years ago to 15 days,” John Hess told the Oil & Money conference on Tuesday.