LONDON - The U.S. needs to levy high taxes on gasoline and to require tougher automobile fuel efficiency standards to conserve energy, the chief executive of one of the country's biggest oil companies said on Tuesday.

John Hess, CEO of Hess Corp which pumps almost 400,000 barrels of oil and gas a day, said the world would face a devastating supply crunch in five to 10 years if it did not limit energy demand and boost supply.

We need to have the courage to demand 50 miles per gallon fuel economy as the national standard for all vehicles, Hess told the Oil and Money conference in London.

The targets we've talked about by the U.S. are way short of what they need to be, he added.

President Barack Obama is currently pushing plans to force automakers to boost average fuel efficiency to 35.5 miles per gallon by 2016.

Hess also advocated higher taxes on gasoline.

A gasoline tax of $1 per gallon would boost conservation and help bring down the federal deficit, he said.

However, Hess cautioned against taking measures to tackle global warming that could limit economic growth. He also cast doubt on the achievability of United Nations' targets to reduce CO2 emissions. (Reporting by Tom Bergin; Editing by David Holmes)