The United States may have reclaimed the title of the world's biggest oil producer sooner than expected.

The U.S. Energy Information Administration said Wednesday that, based on preliminary estimates, America "likely surpassed" Russia in June and August after jumping over Saudi Arabia earlier this year.

If those estimates are right, it would mark the first time since 1973 that the U.S. has led the world in output, according to government figures.

The energy information administration and the International Energy Agency, a global group of oil-consuming nations, had predicted that the U.S. would...