What Drives Oil Prices: OPEC, Inventories, and Demand in Plain English

Oil is the world’s most politicized commodity — the only one with a cartel, a strategic reserve weapon, and the power to swing elections. Yet its price obeys the same law as everything else: supply versus demand, with expectations doing the daily shouting. Here is the framework.

Two prices for one commodity: WTI vs Brent

There is no single world oil price. The two benchmarks that matter are West Texas Intermediate (WTI), the US benchmark priced and delivered at Cushing, Oklahoma, and Brent, the North Sea seaborne crude that serves as the global reference — most of the world’s crude trades at a price set off Brent.

Brent usually carries a premium of a few dollars a barrel over WTI, and the spread typically runs in the low single digits. The gap is a logistics story. WTI is landlocked: it has to reach the Gulf Coast by pipeline or rail before it can be refined or exported. When US production surges faster than pipeline capacity, barrels back up at Cushing and WTI trades at a discount. Brent, loaded straight onto tankers, reflects global supply and demand — and global fear. During the 2011–2013 US shale boom, the bottleneck pushed the Brent–WTI spread past $20 a barrel; in geopolitical flare-ups it has stretched toward $10–17. When a screen says “oil is at $80,” check which benchmark — the answer changes the analysis.

The futures curve: contango and backwardation

Oil’s price at any moment is really a set of prices — one for each delivery month. Plotted together they form the futures curve. When later-dated contracts trade above near-dated ones, the curve slopes upward and the market is in contango. This is the normal state for a storable commodity: someone holding oil bears storage and financing costs, so future delivery costs more. Contango can also signal plenty — if the market is awash in oil, nobody pays up for prompt barrels.

Backwardation is the mirror image: near-dated contracts priced above later ones, a downward-sloping curve. It means the market wants oil now — refineries bidding for prompt supply, inventories drawing — and it punishes stockpiling. Neither shape is a forecast; both describe today’s physical balance. But the shape matters for anyone holding oil exposure: steep contango encourages storage (buy spot, sell forward, pocket the spread), while backwardation rewards holding prompt barrels and penalizes rolling positions forward.

OPEC+: the cartel and its spare capacity

OPEC plus allies including Russia coordinates production quotas covering roughly 40% of global supply — about 43 million barrels a day out of world demand of around 104 million, per the IEA. When OPEC+ cuts, it withholds barrels to defend prices; when it opens the taps, prices sag. Watch the group’s meetings the way equity investors watch earnings — the quota decision versus expectations is what moves the price, and internal cheating on quotas is a permanent subplot.

The cartel’s real power is spare capacity: production that can be brought online within about 90 days and sustained. It is the market’s shock absorber. The IEA’s effective spare-capacity estimate for OPEC+ sits around 4–5 million barrels a day, concentrated overwhelmingly in Saudi Arabia (roughly 1.8 million) and the UAE (roughly 0.7 million). Set against 104 million barrels of daily demand, that buffer is thin — one reason a single disruption can move prices violently. Treat published figures with care: spare-capacity estimates differ across agencies, and voluntary cuts that can be reversed at will are not the same thing as idle, ready-to-pump wells.

The American counterweight: shale

US shale broke OPEC’s old monopoly on marginal barrels. The numbers are stark: American crude production averaged a record 13.6 million barrels a day in 2025, according to the EIA — the highest annual output ever recorded by any country, and about 40% above Russia and Saudi Arabia, the next two producers. The Permian Basin of Texas and New Mexico alone pumps about 6.6 million barrels a day, nearly half the US total. The United States has led world crude production every year since 2018.

Shale responds to price with a lag: high prices bring drilling permits, then new supply 6–12 months later. This lag is why oil cycles overshoot in both directions — the market tightens, prices spike, shale floods in late, and the market tips into surplus.

The Strategic Petroleum Reserve: a policy tool

The US Strategic Petroleum Reserve (SPR) is the world’s largest publicly known emergency oil stockpile. Created in 1975 after the 1973–74 Arab oil embargo, it stores crude in underground salt caverns along the Texas and Louisiana coast. As of September 2026 it held roughly 285 million barrels — about 40% of its 714-million-barrel authorized capacity, per EIA weekly data.

Governments use the reserve as a market weapon, not just insurance. On March 31, 2022, after Russia’s invasion of Ukraine sent prices soaring, the US announced a release of 180 million barrels over roughly six months, at about a million barrels a day — the largest SPR drawdown ever ordered. Releases can cap a fear premium; refilling the caverns later adds demand. Watch SPR announcements as policy signals, priced into the curve within hours.

The weekly reality check: inventories

The EIA’s Weekly Petroleum Status Report lands every Wednesday at 10:30 a.m. Eastern (covering the week ending the prior Friday) and is the market’s most-watched data point. It reports commercial crude stocks, gasoline and distillate inventories, stockpiles at Cushing, refinery utilization, and implied demand. The American Petroleum Institute’s private survey the prior afternoon usually sets expectations — the trade is the headline number versus the forecast, plus the trend against the five-year average.

Falling stockpiles mean demand is outrunning supply (bullish); builds mean the opposite (bearish). The extreme case is storage running out: in April 2020, a full Cushing helped push WTI futures below zero — more on that below.

The demand picture: 104 million barrels a day

Global oil demand ran just under 104 million barrels a day in 2025 and is headed for about 105 million in 2026, per the IEA. Demand tracks economic growth almost one-for-one — recessions kill it, booms feed it — which is why traders read oil, like copper, as a real-time growth signal. China is the marginal buyer whose lockdowns and reopenings have swung prices by double digits. Longer term, the energy transition is a slow bleed on demand growth, but “slow” is doing heavy work in that sentence: oil still fuels the vast majority of transport, and demand has repeatedly surprised forecasters to the upside.

On the supply-risk side: roughly 20 million barrels a day — about a fifth of global petroleum consumption — transits the Strait of Hormuz, per the EIA. Wars, sanctions, and sabotage add a “fear premium” that can appear overnight and evaporate just as fast. The premium is real money while it lasts.

Refining and the crack spread, briefly

Crude is not consumed directly; refineries turn it into gasoline, diesel, and jet fuel. The crack spread — the price of refined products minus the cost of crude — is the refiner’s margin and a useful signal for consumers. The benchmark “3-2-1” crack assumes three barrels of crude yield two of gasoline and one of distillate. A wide crack spread means pump prices can stay firm even when crude falls, and since gasoline is a heavyweight in household budgets, it feeds straight into inflation.

When the market broke: WTI at −$37.63

On April 20, 2020, the May WTI futures contract settled at minus $37.63 a barrel — the first negative print in NYMEX crude futures history, according to the CFTC. COVID-19 had collapsed demand, and the contract expired the next day. Holders of the May contract who could not take physical delivery at Cushing — where tanks were roughly three-quarters full — had to sell before expiry. Traders with storage named their price: pay me to take your oil. The June contract fell hard but stayed positive; the negative print was a delivery-and-storage event, not a verdict that oil was worthless. The lesson endures: when storage vanishes, the physical market overrides every paper forecast.

The dollar link

Crude is priced in dollars worldwide. When the dollar strengthens, oil gets more expensive in every other currency, dampening demand — a reliable headwind; when the dollar weakens, the headwind becomes a tailwind. It is one of the market’s steadier relationships, and one more reason oil traders keep one eye on currency markets.

Reading the price

Don’t ask “is oil going up?” Ask four questions: What is OPEC+ doing versus expectations? Are inventories building or draining? Is global growth accelerating or stalling? Where is the dollar headed? The answers won’t give you next week’s price — nothing will — but they’ll tell you which way the pressure is pushing.

Sources: U.S. Energy Information Administration (Today in Energy, Weekly Petroleum Status Report), IEA Oil Market Report, U.S. Commodity Futures Trading Commission (2020 WTI arbitrage analysis), Reuters, Investopedia.

This article is educational and is not investment advice.