Oil and Gas: Fields, Reserves and Companies

What “proved reserves” means

Reserve numbers are estimates, and the label attached to them matters. Under the industry’s Petroleum Resources Management System, proved (1P) reserves are quantities that are reasonably certain to be recovered from known fields with existing technology and at current economics. Probable reserves are less certain, and proved plus probable is called 2P; when probabilities are used, there should be at least a 90% chance of recovering the proved amount and a 50% chance for 2P. Resources are a wider category still: oil and gas known or thought to exist that can’t yet be produced economically.

Listed companies report reserves under securities rules and audits. National figures are usually supplied by governments and are rarely audited independently, so they can stay unchanged for years even as fields produce. That is worth remembering whenever two sources disagree.

Oil reserves per country

The main public sources are the US Energy Information Administration’s international data (which draws on the Oil & Gas Journal), OPEC’s Annual Statistical Bulletin and the Energy Institute’s Statistical Review of World Energy. Their rankings agree on the leaders but differ in detail, mostly because of how they treat unconventional oil. Venezuela, whose total includes the extra-heavy oil of the Orinoco Belt, and Saudi Arabia report the largest proved reserves. Canada ranks near the top when its oil sands are counted. Iran, Iraq, Kuwait, the UAE and Russia follow.

Large reserves don’t automatically mean large production. Venezuela produces far less than its reserves would suggest, because of investment, sanctions and the cost of handling heavy oil. Our articles on proven oil reserves by country and on the top oil producing countries give the rankings with their sources.

Oman and Qatar

Oman is a mid-sized producer by Gulf standards. The most recent EIA country analysis put its estimated proved oil reserves at 5.4 billion barrels as of January 2018, citing the Oil & Gas Journal, which ranked it seventh in the Middle East (EIA, last updated January 2019). Figures that old should be treated as a guide only. Many of Oman’s fields are mature, which is why enhanced recovery projects matter so much there; our pieces on Oman’s oil and gas projects follow them.

Qatar is a gas country first. Its reserves sit mainly in the offshore North Field, which continues across the maritime border as Iran’s South Pars. QatarEnergy says the North Field holds about 900 trillion cubic feet of recoverable gas, which the EIA describes as making it the largest non-associated natural gas field in the world. Expansion projects on the field are slated to start coming online in 2026. Qatar’s largest crude oil field is the offshore Al-Shaheen (EIA Qatar country analysis, October 2025). See Qatar’s oil and gas reserves for more.

The largest oil and gas fields

A few giant fields hold a large share of the world’s conventional oil. Saudi Arabia’s Ghawar is the largest conventional oil field ever found. Kuwait’s Greater Burgan is usually ranked second, and Saudi Arabia’s Safaniya is the largest offshore oil field. For gas, the North Field and South Pars form by far the largest field, with Russia’s West Siberian giants such as Urengoy also among the biggest. Large new discoveries still happen; the offshore Stabroek block in Guyana, first discovered in 2015, has been the most notable of the past decade. Many of the older giants have produced for more than half a century and are kept going with horizontal wells, water and gas injection and close reservoir monitoring. The hub covers Ghawar, Burgan and South Pars and North Field South in separate articles.

Why reserve figures change

Reserves are not a fixed amount of oil in the ground. They rise when new fields are found, when better recovery methods make more of an existing field producible, or when higher prices make marginal oil economic, and they fall as fields produce or when prices drop. That’s why a country’s reserves can stay flat or even grow for decades while it pumps oil every day, and why it pays to read how each source defines its numbers.

Who holds the reserves, and who explores

Most of the world’s oil reserves are controlled by national oil companies, such as Saudi Aramco, the National Iranian Oil Company, Venezuela’s PDVSA, ADNOC, Kuwait Petroleum Corporation and QatarEnergy. The large listed international companies, ExxonMobil, Chevron, Shell, BP and TotalEnergies among them, produce a lot of oil but hold a much smaller share of global reserves. Saudi Aramco reports the largest reserves of any single company.

Oil and gas exploration services are mostly supplied by contractors: seismic survey firms that image the subsurface, drilling contractors, and service companies such as Halliburton, SLB and Baker Hughes that handle well logging, completion and production technology. Our own satellite work is in metals and industrial minerals rather than oil and gas; if that’s what you’re exploring for, our satellite mineral detection page explains how we rank Exploration Targets on a license.