P10 is the value with a 10% probability that the actual outcome will be at or below it. In cost and schedule risk it is the optimistic end of the range: only one outcome in ten is cheaper or faster. P10, P50 and P90 together describe the spread of a risk model's results.
S-curve. Illustrative QCRA result for a $120m base estimate. The highlighted point is the P10.
How to read P10
On an S-curve, P10 is where the curve crosses 10% on the vertical axis. A P10 cost of $118m means that in 90% of simulated outcomes the project costs more than $118m.
P10 = the value x where P(outcome ≤ x) = 0.10
P10, P50 and P90 together
Level
Chance of coming in at or below
Role
P10
10%
Optimistic bound
P50
50%
Median, central estimate
P90
90%
Cautious bound
The distance from P10 to P90 is the 80% confidence range. A wide range tells a board the estimate is still immature. A narrow range on an early-stage project usually means the model is missing risks or correlation.
The oil and gas reserves convention
Reservoir engineers use the same labels the other way round. P10 reserves are the high case, with only a 10% chance of recovering at least that much. In project cost and schedule work, P10 is the low (cheap, fast) case. Mixing the two conventions in one report is a common and costly error.
Why P10 matters
It tests the base estimate. If the deterministic estimate sits below P10, the plan is more optimistic than 90% of modelled outcomes.
It shows opportunity. The gap between the base estimate and P10 shows how much upside a well-run project could still capture.
It sets the range. Three-point estimates are often better anchored on P10 and P90 than on absolute minimum and maximum values, which experts struggle to judge.
Common mistakes
Using P10 as a target. It is a bound, not a plan.
Confusing P10 with the minimum. One outcome in ten is still lower.
Ignoring the reserves convention when working with upstream colleagues.
P10 is the value with a 10% chance the actual outcome will be at or below it. In cost and schedule risk it is the optimistic end of the range.
What does P10 P50 P90 mean?
They are three points on the S-curve: a 10%, 50% and 90% chance of coming in at or below each value. Together they describe the low case, the median and the cautious case.
Is P10 high or low in oil and gas?
In reserves estimation P10 is the high case. In project cost and schedule risk P10 is the low case. Always check which convention is in use.
Learn to build and defend these models
The QRM Professional Programme teaches QSRA, QCRA and Monte Carlo simulation on real project models in Safran Risk and Primavera Risk Analysis. CPD certified, UK and GCC.
IQRM is a specialist institute for Quantitative Risk Management, delivering
Quantitative Schedule Risk Analysis (QSRA),
Quantitative Cost Risk Analysis (QCRA) and
Monte Carlo simulation training and consulting to major capital projects
across the United Kingdom, Saudi Arabia and the UAE.
Approved Saudi Aramco vendorADNOC approved consultant15+ years applied practice
