The Texas shale revolution will not last forever.

U.S. shale and tight oil production will increase to more than 6 million barrels per day in the coming decade, making up most of total U.S. oil production, according to a recent report by a branch of the U.S. Department of Energy.

U.S. shale oil production has increased significantly since 2010, driven by technological improvements that have reduced drilling costs and improved drilling efficiency. In 2015, oil companies pumped 4.9 million barrels per day out of shale and tight oil fields and, for the first time, made up more than half of total U.S. oil production.

But a report by the Energy Information Administration now says tight oil production will flat line after 2026 as drillers move into less productive oil fields and well productivity decreases.

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South Texas’ Eagle Ford will begin to decline after 2020; North Dakota’s Bakken after 2030, the report says. Production in West Texas’ Permian Basin, which is larger and deeper, remains strong through 2040.

The administration analyzed other scenarios that lead to very different outcomes, the report notes. If technology continues to improve, for instance, tight oil production could rise to 11 million barrels per day or two-thirds of total U.S. output, almost double the baseline scenario. Alternatively, if technology dips, total U.S. oil production would, too, and tight oil would make up less than half of it.