The history of the petroleum industry in the United States goes back to the early 19th century, although the indigenous peoples, like many ancient societies, have used petroleum seeps since prehistoric times; where found, these seeps signaled the growth of the industry from the earliest discoveries to the more recent. Petroleum became a major industry following the oil discovery at Oil Creek, Pennsylvania, in 1859. For much of the 19th and 20th centuries, the US was the largest oil producing country in the world. As of October 2015, the US was the world's third-largest producer of crude oil.