The crash in oil prices has taken its toll. The number of rigs drilling for oil and gas in the U.S. fell today to the lowest level in more than 75 years of records. The animation below shows the deployment of rigs over five years, culminating in the collapse of 75 percent of the rig count.

These five years represent the fastest expansion of oil production in U.S. history. New technology drove this boom—particularly the deployment of horizontal drilling through shale rock. The three biggest oil-producing shale regions are the Permian basin in West Texas, the Eagle Ford in Southern Texas, and the Bakken in North Dakota.

After the plunge in oil prices kicked off in late 2014, producers started shutting down rigs at an unprecedented rate. The number of active oil and gas rigs plunged to the lowest level since Baker Hughes started tracking them in 1940. The rig count fell by 9 in the latest week of data, and now stands at 480. The previous record-low was 488, recorded in April 1999.

A corresponding drop in U.S. production hasn’t yet materialized. Today’s rigs are more efficient, and new wells pump oil faster, so raw rig counts are losing some of their predictive power. Despite the declining number of rigs, the U.S. is still pumping oil at a historically high rate. At some point that will have to change change if rig counts continue to tumble.