Crude oil: Fluctuation in time
Why the oil world must keep running to stand still
What this tab covers How availability changes over seconds, days, seasons, years and longer, how predictable it is, and what that means for the plants that use it.The stock is fixed on human time scales, but each field declines once it peaks. Without continuous drilling world output would fall by about 8% a year.
Variation by time scale
| Time scale | What happens | How large |
|---|---|---|
| Geological | Most oil formed in the Mesozoic. The rest formed in the Cenozoic (about 20%) and Paleozoic (about 10%).3 | 70% formed 252 to 66 million years ago; maturation needs about 10 million years of burial heat |
| Field life (conventional) | After peaking, fields decline at rates set by size and setting.8 | Post-peak decline about 2.7%/yr for supergiant fields, 4.2% onshore, 10.3% deep offshore |
| Tight oil supply without new drilling | Fractured shale wells decline fast, so output depends on continuous drilling.8 | If investment in tight oil and shale gas stopped, output would fall more than 35% within 12 months, then a further 15% |
| World supply without investment | Most upstream spending only offsets decline.8 | Loss of about 5.5 million b/d each year (8%); nearly 90% of upstream investment since 2019 offsets declines |
| Recent decades (US tight oil) | Horizontal drilling and fracking made tight oil the bulk of US output.9 | Tight oil 8.32 million b/d, 64% of US crude output (2023) |
How predictable it is
Field decline is predictable in aggregate. Prices, OPEC+ quotas, geopolitics and the pace of electrification make output decades ahead uncertain.
Crude oil has no weather-driven variability. It is extracted at whatever rate investment, reservoir pressure and policy allow, and stored in tanks and caverns for months. The time pattern that matters is decline. A conventional field may plateau for years and then lose a few percent a year, while tight-oil output as a whole would lose over a third within a year if drilling stopped. So the shale industry must drill continuously just to stand still, but it can also respond to prices within months.
Oil is rarely used to generate electricity outside a few oil-rich or island systems, so plant capacity factors are not a useful measure here.
Sources
- Oil formation Energy Education, University of Calgary, 2023
- The Implications of Oil and Gas Field Decline Rates: Executive summary IEA, 2025
- How much shale (tight) oil is produced in the United States? US EIA, 2024