The programme comes as Exxon, the world's largest publicly traded oil producer, fights accusations by environmentalists and others that it misled investors and the public for years about the risks of climate change from fossil fuels.

Exxon declined to outline the cost of the three-year programme or the savings it projects by keeping methane from venting. Methane is a component of natural gas and can be sold.

"We do believe this will have a meaningful impact on our methane-emissions reductions," said Sara Ortwein, president of XTO Energy, Exxon's shale-focused subsidiary. "We remain committed to minimizing our environmental impact from our operations."

As part of the three-year programme, Exxon will replace outdated natural gas-powered pneumatic pumps, which chronically leak methane into the atmosphere, with compressed air-powered pumps. Such pumps can regulate pressure, temperature and other variables in oilfield equipment.

The company will also boost employee training on methane emissions reduction and begin to study how satellites, drones and other equipment can better be used to detect leaks.

Exxon said it has worked with the National Oceanic and Atmospheric Administration on using drones for methane detection flights.

The programme has received praise from some environmental groups, who said Exxon is taking a step to curbing greenhouse gas emissions.

"It sounds like a very robust programme," said Matt Watson of the Environmental Defense Fund. "We're eager to get more details."

(Reporting by Ernest Scheyder; Editing by Bernadette Baum)