What ARE THE types of oil reserves?

Oil reserves are primarily a measure of geological risk - of the probability of oil existing and being producible under current economic conditions using current technology. The three categories of reserves generally used are proven, probable, and possible reserves.

Proven reserves - defined as oil and gas "Reasonably Certain" to be producible using current technology at current prices, with current commercial terms and government consent- also known in the industry as 1P. Some Industry specialists refer to this as P90 - i.e. having a 90% certainty of being produced.

Probable reserves - defined as oil and gas "Reasonably Probable" of being produced using current or likely technology at current prices, with current commercial terms and government consent - Some Industry specialists refer to this as P50 - i.e. having a 50% certainty of being produced. - This is also known in the industry as 2P or Proven plus probable.

Possible reserves - i.e. "having a chance of being developed under favourable circumstances" - Some industry specialists refer to this as P10 - i.e. having a 10% certainty of being produced. - This is also known in the industry as 3P or Proven plus probable plus possible.