Oil is a nonrenewable resource, which is available only in finite quantities, and it will eventually become uneconomical to extract. New technologies, such as hydraulic fracturing, have delayed that point for several decades, but the total volume of oil is not increasing, according to the U.S. Department of Energy.
The amount of oil left to be extracted is measured in different ways. The total amount of oil buried in the Earth's crust is not known with certainty, but as of 2013, proven reserves stood at around 1.646 trillion barrels of crude oil, according to the U.S. Department of Energy. This figure is somewhat higher than 2012's 1.526 trillion barrels, which is itself higher than 2011's total figure. The reason proven oil reserves seem to be increasing each year is that aggressive exploration is turning up new pockets of oil faster than the oil is being consumed.
Regardless of current reserves, the rate at which oil reservoirs can be recharged is so low that human industry is gradually reducing the total amount on Earth. Most of the oil being extracted today was laid down around 100 million years ago, according to Livescience. Depending on conditions, oil can take anywhere from 1 million to 1 billion years to form, so while humans are unlikely to extract every last drop of crude oil, reserves will continue to be depleted until not enough is left to justify further extraction efforts.