I'm afraid I still haven't grasped the P10, P50, P90 system...

I'm afraid I still haven't grasped the P10, P50, P90 system yet

P50 means if there is hydrocarbons present, there is a 50% chance there being more hydrocarbons in the structure than the published P50 value.

Similarly, P90 means if there is hydrocarbons present, there is a 90% chance there being more hydrocarbons in the structure than the published P90 value. Therefore the P90 value is always less than the P50 value.

Again, similarly, P10 means if there is hydrocarbons present, there is a 10% chance there being more hydrocarbons in the structure than the published P10 value. Therefore the P10 value is always more than the P50 and P90 values.

They presumably determine the P10, P50 and P90 figures by interpreting the seimic surveys of the shape of the structure to be drilled.