While president, Obama lifted a ban on exporting crude oil that had been in place since 1975.

That ban was put in place in response to the 1973 oil crisis, where OPEC countries placed an embargo on oil sales to countries they felt were supporting Israel in the Yom Kippur War. The price of oil shot through the roof, and the U.S. decided that we needed to do whatever we could to make sure we'd have a steady supply of oil that wasn't vulnerable to those sorts of actions. And thus, the export ban was put into place, much to the chagrin of oil companies who didn't care about any of this bullshit.