What it means
Reserve reporting exists because an underground resource cannot be counted the way finished goods in a warehouse can; engineers estimate it from well data, seismic surveys, core samples and production history. The tiers express confidence, with proved reserves carrying roughly a 90% chance of being recovered, the 2P case around 50% and the 3P case about 10%.
Only proved reserves normally feed the audited financial statements and the depletion charge, so 3P figures tend to appear in investor presentations and technical reports rather than in the accounts. That difference in standing is the single most important point for a non-specialist reader.
Analysts use 3P as a sensitivity case rather than a forecast. A valuation might be built on the 2P estimate, with 1P as the downside and 3P as the upside, each multiplied by an expected cash margin per unit to produce a range of asset values.
The tiers are cumulative rather than separate buckets: 2P equals proved plus probable, and 3P equals proved plus probable plus possible. Quoting 3P alongside 1P without explaining that overlap is a classic source of double counting in a spreadsheet.
Definitions are set by industry standards and securities regulators, and a barrel only counts as a reserve if prices and technology make extraction commercial. A price slump can therefore move volumes out of the reserve count without a single physical change underground.
In practice
Real-world examples.
Example
A mid-size exploration company raising $80 million leads its investor deck with a 3P figure of 25 million barrels. A careful analyst rebuilds the model on the 2P case, finds the funding plan still works, and recommends subscribing on that basis rather than on the headline.
Example
A bank lending against a producing field sets its borrowing base on proved reserves only and ignores the 3P number entirely. The available loan therefore barely moves when the company announces an upgraded possible reserve estimate.
Example
A mining group reports lower reserves after a fall in metal prices, even though its drilling results improved that year. Part of the deposit became uneconomic at the new price, so tonnes moved out of the reserve count and the 3P total fell with them.
Formula
Calculation
1P = proved reserves. 2P = proved + probable. 3P = proved + probable + possible.
A company reports proved reserves of 12 million barrels, probable reserves of 5 million barrels and possible reserves of 8 million barrels. That gives 2P = 12 + 5 = 17 million barrels and 3P = 12 + 5 + 8 = 25 million barrels. If the expected net cash margin is $20 a barrel, the indicative asset value runs from 12 million x $20 = $240 million on a 1P basis, through 17 million x $20 = $340 million on 2P, to 25 million x $20 = $500 million on 3P. Presenting only the $500 million figure, without saying it rests on the least certain tier, is how reserve numbers mislead.Case study
Seen in the real world.
Kestrel Basin Energy is an invented company offered here as an illustrative case. In the story it raised money on a prospectus that highlighted 3P reserves of 40 million barrels while proved reserves stood at just 9 million.
Two years later the fictional company had produced far less than investors expected, because the possible tier included volumes in a geologically awkward flank of the field that appraisal drilling did not support. The share price halved, and the board rewrote its reporting policy to lead with the 2P case and show all three tiers side by side.
The illustrative point is not that 3P figures are dishonest, since they are a recognised measure, but that a number carrying roughly a one in ten chance should never be presented as the expected outcome.
Watch out
Common mistakes.
- Treating 3P as expected production, when it is an optimistic upper case with a low probability attached to it.
- Adding 1P, 2P and 3P together, which counts the same proved volumes three times over.
- Expecting 3P reserves to appear in audited financial statements alongside proved reserves and depletion charges.
Questions
People also ask.
What does the P stand for?
It refers to the probability tiers of proved, probable and possible reserves, and the number shows how many of those tiers are included in the total.
Which measure should a lender or investor rely on?
Lenders usually work from proved reserves, while equity investors often value on the 2P case and treat 3P as upside, so every reserve number should state its basis.
Can reserves fall without any production?
Yes, lower prices, higher costs or disappointing appraisal results can make part of a resource uneconomic and push it out of the reserve count.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%