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Reserve Calculator


Slide the sliders of each variable to whatever levels you desire and watch your oil estimate change based on where each slider comes to rest. Keep in mind that this is a rudimentary estimator using the standard variables of the geologist's method of estimation, not a rigorous, reliable estimator of any given oil field. It is designed to help you see how changes in each variable affect the total volume of oil in place and how much might be recoverable. We have provided tabs on the extent variable to contextualize the sizes of a few well-known formations.


This is the area of the formation in square miles.


This is the thickness of the formation in feet.


How much space in the rock is available for fluids? This is a percentage of the total volume of the formation. We've limited this variable to 50% because not many formations have porosities higher than that. Unconventional formations are lucky if their porosities reach 5%.

Water Saturation

How much of the porosity is filled with water? This variable goes to 100% because it is possible for all the pore space in the formation to be filled with water. If that is the case, there will be no oil or gas.

Recovery Factor

After all of the above values are determined, that gives us the total oil and gas in place. We now have to adjust for the recovery factor which is the percentage of the hydrocarbons in place that are able to be extracted economically with existing technology. This variable is limited to 80% because there is always some volume of hydrocarbons left in the formation. Some unconventional plays like the Marcellus may top out at recovery factors of 30%, while more traditional formations treated with care and enhanced recovery techniques may approach 80%.

Reference: Hyne, Norman J., 2001, Nontechnical Guide to Petroleum Geology, Exploration, Drilling, and Production, 2nd Edition (accessed July 1, 2015)