Oil reserve refers to the deposits of oil found in the Earth which are known to exist. Moreover, they must be economically feasible and technologically possible to extract. Oil reserves are found in various countries, however, the majority is concentrated in the Middle East.
One way to think about the size of reserves is known as the reserves/production ratio or R/P. This number represents the number of years that the reserves would last if production and use was continued at the current rate.
The R/P ratio for oil reserves is smaller than coal and natural gas reserves. As of 2017, estimates suggest that at current use there is around 50 years worth of oil remaining. However, this ratio needs to be interpreted carefully as this assumes current production levels. Production could increase in the coming years, or decrease as alternative fuels become more prominent. In addition, this number doesn't take into account of changing prices or developments that allow fuel to be extracted from current resources.
Oil is one of the most vital natural resources for modern society. Oil is used extensively for transportation and as a petrochemical feed-stock to make many items like medicine and fertilizer. It provides a vast amount of goods and services worldwide, however, the distribution of the oil reserves worldwide are not even. The Middle East holds around 64% of the worlds crude oil reserves, with Saudi Arabia alone accounting for nearly a quarter of all reserves worldwide. Conversely, the largest oil consumer—the United States—has less than 2% of the worlds's oil reserves, but consumes more than one-fifth of the total consumption of oil worldwide. Estimates claim the world's oil reserves range from 1.2 to 1.4 trillion barrels. This is equal to around 6000 EJ, or 6000 quads. Advances in drilling technologies have resulted in more oil becoming "reserve oil" as it becomes economical to extract. Below is a chart showing where the world's oil reserves are located.
Press the play button on the simulation below to see how the oil reserves have changed over the last few decades.
Aside from traditional deposits, there are other places that crude oil can be gathered from. Generally speaking these deposits are less economical to mine as they require more advanced technology and more effort to extract and process the fuels for use. Nevertheless, as technologies advance the ability to obtain fossil fuels from these deposits becomes more economic, leading to increased reserves (although the occurrence of this resource is still decreasing).
There are several different types of unconventional oil reserves. The oil sands are one example of an unconventional resource as bitumen-soaked sand is dug up and the bitumen is extracted and upgraded to yield crude oil. This process is more labour-intensive than obtaining crude oil from wells, but possible. The province of Alberta alone contains around 1.6 trillion barrels of oil in the oil sands, more than the world's reserves of crude oil. However, only 10% is currently economic to extract. Additionally, shale oil can be obtained by utilizing hydraulic fracturing to break apart oil shale. The shale is then put under extreme pressures and temperatures to extract oil. Rough estimates put the amount of oil locked into oil shale at 1 trillion barrels in the United States alone, approximately equal to the proven world reserves of liquid crude oil.