There are various different levels of "proven" oil reserves (P1,...

There are various different levels of "proven" oil reserves (P1, P2, P3) for crude oil reserves. They can be summarized as follows:

Proved 1P - at least 90% probability
Proved + Probable 2P - at least 50% probability
Proved + Probable +Possible 3P - at least 10 % probability

However, to make things more confusing, some people do not use the definition of geological probability for the existence of an oil reserve, but vague assertions like:

Proved P1 - reasonable certainty
Probable P2 - more likely than not
Possible P3 - less likely than probable