Hydrocarbon Reserves and Resources

Oil and gas reserves are the remaining quantities of oil and gas that can be produced using existing and planned production facilities under existing commercial terms.  Contingent and Prospective Resources are volumes of oil and gas that may be converted into reserves if matured. For all Reserves and Resource estimates there is a range of uncertainty and it is important to quote the range of uncertainty to understand the up- and downside associated with specific development plans. Cubes3 staff can provide Competent Persons Reports (CPR) and create Reserves Reports.

Reservoir sand

Proved Reserves

Proved Reserves are the volumes of oil and gas that remain in the reservoir according to the definitions of the SPE, AIM or the Securities and Exchange Commission (SEC) in the USA. These volumes are calculated according to the agreed rules and provide a conservative, low estimate of reserves. They are split in developed and undeveloped volumes.  The Standardised Measure is an independent valuation method, which helps investors to compare the value of Proved Reserves of different oil companies at clearly defined oil and gas prices.

Probable and Possible  Reserves

Probable Reserves are the volumes that are expected to be produced from the reservoir using existing and approved facilities, based on existing contracts. Possible Reserves represent the high side of the probability distribution of reserves. As with Proved and Probable Reserves a distinction is made between developed and undeveloped reserves.

Contingent Resources

Contingent Resources (CR) are oil and gas volumes which may be developed if an economic development plan can be proposed and approved. Contingent Resources may be subdivided into categories such as CR pending development, CR non-viable and CR on hold to reflect the various stages of technical and commercial maturity of a project.

Prospective Resources

Prospective Resources are undiscovered volumes of oil and gas, which have been identified by exploration geologists. Prospective Volumes may be subdivided in Prospect, Lead and Play volumes to reflect the relative maturity.  The volumes are defined using a Mean Success Volume and the Probability of Success and have a large range of uncertainty.


Cubes3 provides training and assistance for the calculation of reserves and resources. Training courses can be focussed on Exploration staff, Geologists, Reservoir Engineers, Economists or Finance staff depending on their role in the reserves calculation process.