Uranium Resources and Reserves: Definitions Explained

Reference article · Updated 2026-11-06

Key facts

Identified resources in the OECD-NEA/IAEA Red Book equal reasonably assured plus inferred resources, tabulated by production-cost class.
The Red Book edition reported in 2025 gives about 5.86 million tU of identified resources recoverable below USD 130/kgU, and about 8.1 million tU below USD 260/kgU.
Company reports use JORC (Australasia) or NI 43-101 (Canada) categories, which are not identical to Red Book categories.
A resource is not a reserve: reserves require demonstrated economic viability under stated assumptions.
Secondary supplies such as stockpiles, recycled material and re-enriched tails are counted separately from mined resources.

Why one deposit can carry several different tonnages

Statements such as "the world holds X million tonnes of uranium" are only meaningful together with three qualifiers: the confidence in the estimate, the cost ceiling used to decide what is worth extracting, and the date of the assessment. Change any of them and the number changes, even though the rock in the ground has not.

Two families of classification are in everyday use. National and international statistical publications, above all the joint OECD Nuclear Energy Agency and International Atomic Energy Agency report commonly called the Red Book, group resources by geological confidence and by production cost. Mining companies listing on stock exchanges, by contrast, follow codes such as JORC or Canada's NI 43-101, which are designed to protect investors and are written around the concepts of competent persons and public reporting.

For the market context in which these figures are used, see Uranium Production and Demand.

Red Book categories: identified, undiscovered and cost classes

The Red Book, published roughly every two years, collects data supplied by national authorities. Its resource scheme has two main branches.

Identified resources are deposits whose size, grade and configuration are known to a degree that permits an estimate. They comprise reasonably assured resources (RAR), where confidence is highest, and inferred resources, where tonnage and grade rest on more limited information.
Undiscovered resources are inferred from geological knowledge rather than from drilling of specific deposits. They are usually split into prognosticated and speculative resources, in order of decreasing confidence.

Each identified category is tabulated by the cost of production. The cost classes that recent editions emphasise are resources recoverable below USD 130 per kilogram of uranium and below USD 260 per kilogram of uranium. These are cost ceilings used for classification, not market prices, and they are expressed in contemporary US dollars of the reporting year, so they are not directly comparable across decades.

The edition reported in 2025, with data as of 1 January 2025, gives identified resources of about 5.86 million tonnes of uranium (tU) in the below-USD 130/kgU class and about 8.1 million tU in the below-USD 260/kgU class, according to the World Nuclear Association's summary of the report. Australia is the country with the largest share in the lower cost class.

Tonnes of uranium, tonnes of U3O8 and pounds

Resources are normally stated as tonnes of contained uranium metal (tU). The market, however, trades in pounds of U₃O₈, the oxide concentrate sometimes called yellowcake. Uranium makes up about 84.8 per cent of the mass of U₃O₈, so one tonne of U₃O₈ contains about 0.848 tonnes of uranium, and one tonne of uranium corresponds to roughly 1.18 tonnes of U₃O₈. One pound is 0.45359237 kilograms.

Always check which basis a statement uses. Mixing tU with tU₃O₈ inflates or deflates a figure by about 18 per cent. The calculators on this site, for instance in the material balance page, use the same conversion constants.

Resource versus reserve in company reporting

Under JORC and NI 43-101 a mineral resource is a concentration of material with reasonable prospects for eventual economic extraction, classified as inferred, indicated or measured in order of increasing geological confidence. A mineral reserve is the part of a measured or indicated resource that a study has shown to be economically mineable after applying modifying factors such as mining method, metallurgical recovery, costs, permitting and social licence. Reserves are classed as probable or proved.

Two practical consequences follow. First, inferred resources cannot be converted directly into reserves; further drilling must first raise confidence. Second, a project's reserve depends on assumed prices and costs, so the same deposit may move in and out of the reserve category as these change.

The Red Book's RAR category broadly corresponds to measured plus indicated, and its inferred category to inferred, but the mapping is approximate. Resource tables in the Red Book are national reports and are not audited statements under investor codes.

Deposit type shapes the numbers

Resources are also reported by deposit type, because grade, mining method and cost differ widely. Examples in the Red Book typology include unconformity-related deposits (such as those of Canada's Athabasca Basin), sandstone deposits suited to in-situ leaching, iron-oxide copper-gold deposits where uranium is a by-product, intrusive and volcanic types, and various others. Cost ceilings are heavily influenced by the type: a high-grade underground deposit and a low-grade sandstone ISL deposit are not directly comparable by tonnage alone.

Regional pages on this site describe where these types occur, for example the mining map overview and the explainer on in-situ leaching. By-product recovery from copper or gold operations is described on the Olympic Dam page.

Secondary supplies sit outside the resource base

Mined resources are not the only source of fuel. The World Nuclear Association identifies several secondary supplies: civil inventories held by utilities and governments, down-blended military material (a major source from 1987 until the early 2010s), recycled uranium and plutonium from reprocessing, re-enrichment of depleted uranium, and "underfeeding" at enrichment plants, where less enrichment work is used per unit of product and more natural uranium is consumed in the feed. These supplies are reported in supply statistics but are not part of Red Book resources.

For the enrichment and tails arithmetic behind underfeeding, see the enrichment and SWU calculator.

A checklist for reading a resource statement

Identify the system. Is it Red Book, JORC, NI 43-101, a national code or a promotional estimate?
Check the category. Inferred and undiscovered tonnage should not be added to measured and indicated tonnage without saying so.
Note the basis. Contained uranium or U₃O₈; in-situ or recoverable; 100 per cent of the project or the company's attributable share.
Look at the cost ceiling or price assumption. A cut-off grade only makes sense with the price and cost assumptions behind it.
Check the date. Depletion by production and re-estimation make older numbers stale.
Look for an independent qualified person. Investor codes require a named competent or qualified person to sign off the estimate.

Cut-off grade and recovery assumptions also drive project economics, illustrated with user-supplied numbers in the mine feasibility calculator.

Frequently asked questions

What is the difference between a uranium resource and a reserve?

A resource is mineralisation with reasonable prospects of eventual economic extraction, classified by geological confidence. A reserve is the portion shown by a study to be economically mineable under stated assumptions, so it is a narrower and more assumption-dependent number.

What does the Red Book measure?

The Red Book, produced by the OECD Nuclear Energy Agency with the IAEA, compiles national reports on uranium resources, production and demand. Its resource tables are grouped by confidence category and by production-cost class.

Why are there different figures for world uranium resources?

Figures differ because of cost ceilings (for example below USD 130/kgU versus below USD 260/kgU), because identified and undiscovered resources are counted differently, and because publication dates differ.

Are uranium resource figures given as uranium or U3O8?

Official statistics normally give tonnes of uranium metal, while markets use pounds of U3O8. Uranium is about 84.8 per cent of U3O8 by mass, so the two bases differ by roughly 18 per cent.

Do stockpiles and recycled fuel count as resources?

No. Inventories, down-blended material, recycled uranium and re-enriched tails are secondary supplies. They are reported alongside, but separately from, mined resources.