Reserves vs resources: what the two words mean

Published 2026-10-08; updated 2026-10-08.

Ask how much copper, oil or lithium is left and you will get two kinds of answer. One is a reserve figure, which is smaller and changes often. The other is a resource figure, which is larger and less certain. They are different categories in a classification system, not the same quantity described cautiously or boldly.

What do USGS and the petroleum industry mean by the two words?

The U.S. Geological Survey sets out its definitions in Appendix C of the Mineral Commodity Summaries 2026, based on a 1980 classification worked out with the then U.S. Bureau of Mines (USGS Circular 831). In paraphrase:

• A resource is a concentration of a solid, liquid or gas in or on the Earth’s crust, in a form and amount that makes economic extraction currently or potentially feasible.
• Identified resources are those whose location, grade, quality and quantity are known or estimated from specific geologic evidence. Undiscovered resources are those whose existence is only postulated.
• Reserves are the part of the identified resource that could be economically extracted or produced at the time the estimate is made. Extraction facilities need not be in place.
• Resources that fail the economic test today are called subeconomic. They may pass it later.

The oil industry draws the line in similar places with different tools. The Society of Petroleum Engineers’ guide to its Petroleum Resources Management System (2007) says reserves are the commercially recoverable part of resources that has been justified for development, with contingent and prospective resources less certain. The U.S. Securities and Exchange Commission, in rule 17 CFR 210.4-10, defines proved reserves as quantities with reasonable certainty of recovery under existing economic conditions, operating methods and regulations, with prices set as a twelve-month average. The words share a root and carry different tests, so the figures of one system cannot be added to another’s.

Why do reserves change when nothing has been mined?

Because the economic test moves. USGS says in the same appendix that reserves data are dynamic and may be thought of as a working inventory: a mining company develops reserves to the point its business needs, limited by drilling cost, taxes, the price of the commodity and demand for it. They shrink as ore is mined or becomes uneconomic, and more often grow as deposits are developed, explored further, or helped by new technology or better economics.

USGS gives its own example. In 1970, it says, identified and undiscovered world copper resources were estimated at 1.6 billion tonnes of contained copper, with reserves of about 280 million tonnes. USGS adds that about 712 million tons of copper have been produced worldwide since 1970, yet its reserve estimate of 980 million tons is more than 3.5 times the 1970 figure (Appendix C).

What does the data show?

This site’s how much is left table compares USGS’s world reserve tables across editions and subtracts what was mined in between. Of 18 minerals that can be checked, reserves are larger in the 2026 edition than in the 2023 edition (a 2022 figure) for 14, even after about three years of mining.

Copper is the plainest case. Reserves were 890 million tonnes in the 2023 edition and 980 million tonnes in 2026, about 10% higher, although the 2024 edition printed 1,000 million. World mine production was 22.6, 23.0 and 23.0 million tonnes in 2023, 2024 and 2025, a total of 68.6 million. Add that back and USGS’s estimate has grown by 158.6 million tonnes in three years: more was counted than was mined. USGS also gives resources for copper: a 2015 assessment found 1.5 billion tonnes of identified, unextracted copper and an estimated 3.5 billion tonnes undiscovered. Reserves of 980 million tonnes are only part of the first figure.

For four minerals the figure went the other way by more than mining: rare earths, graphite, vanadium and bauxite. Rare earths fell from 130 million tonnes in 2022 to about 75 million tonnes (USGS prints a world total of “more than 75 million”, so this is a lower bound; the site’s data use 75.29), a drop of about 54.7 million tonnes against about 1.15 million tonnes mined. Mining explains only a small share, about 2%. Vanadium fell from 26.0 million tonnes to about 21 million (USGS prints 21.0; the country rows sum to 21.5) while 0.34 million were mined, under 8% of the drop. USGS’s 2026 notes say reserves for Australia, Brazil and Malaysia were revised for rare earths “based on Government reports”, and for vanadium reserves for Australia, Brazil, China, South Africa and the United States were revised based on company and Government reports (USGS rare-earths chapter and vanadium chapter). The data here cannot tell how much of each fall those revisions explain, so this site does not assign a cause.

Fuels show the same pattern over a longer span. The Energy Institute counts world proved oil reserves (including natural gas liquids) of 683 billion barrels in 1980 and 1,732 billion barrels at the end of 2020, while about 1,093 billion barrels of oil (crude oil, shale oil, oil sands and natural gas liquids) were produced in the years between. Oil reserves rose by 154% even as output ran at more than 20 billion barrels a year.

Which one should you use?

Use reserves when the question is what is being counted as extractable, and for comparing countries: the reserves pattern page sets each country’s share of reserves against its share of mining. Use resources when the question is what could one day be reserves, and accept that the figures are rougher. Neither is a measure of what physically exists: the glossary entry for reserves makes the point that the same deposit can be large in the ground and small on the books.

Two cautions apply to every table of reserves. They rest on estimates assembled from national agencies, companies and trade sources, with differing definitions (USGS notes Australia reports a different category, “Economic Demonstrated Resources”, and Russia uses a Soviet-era system). And the years of supply they imply are a ratio, not a date: see the reserves-to-production ratio, and for what a peak in output means, peak oil vs peak copper.

Cite as: Commodity Origins, "Reserves vs resources: what the two words mean", https://commodityorigins.com/learn/reserves-vs-resources/ (CC BY 4.0).