Reserves are deposits of fossil fuels that are known to exist with a reasonable level of certainty based on geological and engineering studies. These reserves are also recoverable economically with the technologies that already exist.
Although both resources and reserves refer to some amount of a mineral or fuel, they are not the same thing and should not be confused as they are very different. This difference can be explored using a McKelvey diagram. McKelvey diagrams portray information about how a resource can turn into a reserve over time with effort.
There are different reserves for all fossil fuels which are distributed around the globe in different areas and different amounts. Although these numbers may seem precise, they are still a rough estimate of what exactly we know to exist and have the ability to extract economically. One way to determine 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.
Oil is one of the most vital fossil fuels, and the distribution of the reserves worldwide is 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 reserves while contributing to more than one-fifth of the total consumption of oil worldwide. Estimates put the worlds oil reserves in the range of 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.
Coal is the most abundant of all the fossil fuels, and therefore there is a significant amount of coal in reserves worldwide. Although these areas are spread out - with major reserves in the United States, Russia, China, Australia, and India - there is still a significant amount of coal in reserves, around 1012 tonnes. Coal reserves have the largest R/P ratio of 120 years, meaning that if production rates remain the same the current coal reserves will last 120 years. Below is a chart showing where the world's coal reserves are located.
Natural gas tends to form with crude oil, although the quantities of oil and gas do not always relate. For example, Saudi Arabia has massive oil reserves but is comparable to the United States in its gas reserves. The world's reserves of natural gas are estimated to be around 6 quadrillion cubic feet, which amounts to 6000 EJ, the same as the world's oil reserves. 40% of all conventional natural gas reserves are located in the Middle East, and 30% is in the former Soviet Union. Below is a chart showing where the world's natural gas reserves are located. Press the play button to see how the natural gas reserves in the world have changed in the past few decades.
Aside from traditional deposits, there are other places that crude oil and natural gas 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 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.
For natural gas, shale gas, tight gas, and coal bed methane deposits are all unconventional sources of fossil fuels as they require hydraulic fracturing or water pumping to extract the gas from the deposits.