Crude oil is a complex mixture of hydrocarbons that must undergo transformation at a petroleum refinery before use. The standard unit of measure for this commodity is the 42-gallon barrel, which serves as the baseline for calculating the output of refined products. The refining process separates and chemically alters the crude oil’s components to create a diverse range of fuels and materials.
Defining the Standard Barrel and Refining Gain
The 42-gallon barrel is the universally accepted measure for crude oil input into a refinery. When this volume is processed, the total volume of finished products exiting the refinery is consistently greater than the initial 42 gallons. This phenomenon is known as refining gain.
This volume increase occurs because the refining process converts heavy, dense hydrocarbon molecules into lighter, less dense ones, such as gasoline and diesel. On average, a 42-gallon barrel of crude oil yields approximately 44 to 45 gallons of refined products, representing a volume increase of around 6%.
The Primary Liquid Fuel Yields
Transportation fuels, which have the highest demand, account for the largest share of the refined barrel, roughly 70% of the total volume. From one 42-gallon barrel of crude oil, refineries typically produce about 19 to 20 gallons of motor gasoline. Gasoline is composed of hydrocarbons with lower boiling points, making it suitable for spark-ignited internal combustion engines.
The second most significant product is ultra-low sulfur distillate fuel oil, yielding approximately 11 to 12 gallons per barrel. This fraction is primarily sold as diesel fuel, but a portion is also used as heating oil. Together, gasoline and diesel represent the bulk of the barrel’s output.
Quantifying the Secondary Distillates and Residues
The remaining 20% to 30% of the barrel consists of secondary distillates and heavier residues. Jet fuel, specifically kerosene-type jet fuel, is a notable middle distillate, typically yielding around 4 gallons from the 42-gallon input. This fuel is chemically similar to kerosene but meets the specifications required for turbine engines in aircraft.
Heavier products, such as residual fuel oil, generally yield about 1 to 2 gallons. Residual fuel oil is used in large marine vessels and industrial applications that require a heavy, high-viscosity fuel. Liquefied Petroleum Gases (LPG), including propane and butane, are among the lightest products and typically account for about 2 gallons of the final output.
The remaining volume is distributed among several specialized products:
- Lubricating oils, used to minimize friction in machinery.
- Waxes, used in packaging and candles.
- Asphalt and road oil, the heaviest non-gaseous residue, used for paving roads and roofing materials.
- Petrochemical feedstocks, such as naphtha, isolated for use as raw materials in manufacturing plastics and synthetic rubber.
Why Product Yields Are Not Fixed
The specific volumes listed are national averages and are not fixed, as the composition of the refined barrel is highly variable. One primary factor is the type of crude oil being processed, known as the crude slate. Light and sweet crude oils naturally contain a higher proportion of the smaller molecules needed for gasoline and diesel. Conversely, heavy and sour crudes have more large, complex molecules, requiring extensive processing to yield lighter products.
The complexity of the refinery itself also introduces significant variability into the product mix. Simple refineries rely mainly on atmospheric distillation to separate components by boiling point. More complex facilities employ advanced conversion units, such as fluid catalytic crackers or hydrocrackers. These units can chemically break down heavy residual oils into higher-value products like additional gasoline and diesel, allowing refiners to adjust output based on market demand.