What is a Barrel?

The oil barrel equals exactly 42 US gallons (158.987 liters) and is the global benchmark unit for crude oil pricing and trading. The 42-gallon size dates to the 1860s Pennsylvania oil boom, when oil was shipped in repurposed wooden barrels of various sizes; the standard settled at 42 gallons as a practical industry compromise. Today, the oil barrel is virtually synonymous with crude oil — Brent crude and WTI prices are quoted per barrel ($/bbl), OPEC tracks production in barrels per day, and proven reserves are listed in billions of barrels. Despite metrication, the barrel persists in petroleum trading and journalism worldwide. It relates to the US gallon (1 bbl = 42 US gal), the cubic meter (1 bbl ≈ 0.159 m³), and the liter (1 bbl ≈ 159 L). Note that beer and wine barrels have different volumes.

Visual reference for how the barrel relates to other volume units. Each row links to the full converter for that pair.

See all 15 volume units in matrix view →

• Crude oil international pricing (Brent, WTI)
• Petroleum product reporting (OPEC, EIA)
• Energy-sector financial reporting

• ✓1 oil barrel = 42 US gallons = 158.987 L exactly.
• ✓Barrel prices quoted in USD — watch currency impact on non-US economies.
• ✓Different industries (beer, dry goods) use different barrel sizes — oil barrel is a specific unit.

• ✗Using beer barrel (163.7 L) or dry barrel (115.6 L) in oil contexts.
• ✗Confusing barrel of oil with barrel of beer — different volumes.
• ✗Assuming barrels are standard worldwide — only oil industry uses the 42 gallon version globally.