It looks like there was a slow drop-off from about 2017 onward. The big drop started early 2022, likely related to Russia's invasion of Ukraine.

The Biden administration (and other countries around the world in the International Energy Agency) released reserves to try to stabilize the spikes in prices due to the Russian invasion of Ukraine.

> On March 1, 2022, Secretary Granholm announced that the U.S. and its partners in the International Energy Agency (IEA) would release a total of 60 million barrels of oil onto the world market. [snip] In total, DOE released 180 million barrels of crude oil into the market.

https://www.energy.gov/hgeo/opr/history-spr-releases (look at 2022 IEA Coordinate Release)

Same reason as today, trying to counter high energy prices.

Trump got all the oil producers together in a room and put together a deal to restrict oil production during COVID.

This, naturally, resulted in higher oil prices, which the Republican party blamed Biden for.

They truly have no shame.