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When leaders from Exxon Mobil and BP gathered last month with other fossil-fuel executives to declare they were serious about climate change, they cited progress in curbing an energy-wasting practice called flaring — the intentional burning of natural gas as companies drill faster than pipelines can move the energy away.

But in recent years, some of these same companies have significantly increased their flaring, as well as the venting of natural gas and other potent greenhouse gases directly into the atmosphere, according to data from the three largest shale-oil fields in the United States.

The practice has consequence for climate change because natural gas is a potent contributor to global warming. It also wastes vast amounts of energy: Last year in Texas, venting and flaring in the Permian Basin oil field alone consumed more natural gas than states like Arizona and South Carolina use in a year.

Exxon’s venting and flaring has surged since 2017 to record highs, both in absolute terms and as a proportion of gas produced, the numbers show. Exxon flared or vented 70 percent more gas in 2018 than it did the previous year, according to the data, bringing an end to several years of improvements.