Gasoline is one of the major petroleum products produced from processing crude oil in a petroleum refinery.

Gasoline is one of the higher-valued clean products (along with jet fuel and diesel). It is used almost exclusively in the transportation sector, mostly as a fuel in automobiles and other light-duty vehicles. Generally, refiners will try to maximize their yield of gasoline, along with diesel, to maximize profit. Since the two products draw from different boiling range material, they are largely complimentary. However, there are a few conversion units that favor one over the other, forcing refiners to make a call on which will be more value-creating. Most notably, FCCs will tend to upgrade VGO more toward gasoline, and hydrocrackers will upgrade VGO more toward diesel.

Gasoline product qualities

Gasoline powered vehicles use Otto cycle (spark ignition) engines. To perform well and to minimize environmental impact, this requires gasoline to have specific product qualities. Some of the more important ones are:

octane - a measure of a fuel's resistance to auto-igniting (knocking) when compressed with air in a spark ignition engine

vapor pressure - a fuel's volatility or tendency to vaporize 

distillation profile - This describes how much of gasoline (volume %) evaporates at different temperatures

vapor lock index - measures the tendency of gasoline to vaporize in the fueling system, causing vapor lock

driveability index - a measure of a fuels performance at both cold start and warmed-up conditions

sulfur content - measure of the sulfur remaining in the fuel 

aromatics content - aromatics compounds include high-octane materials such as benzene, toluene and xylene

benzene content - benzene is a known carcinogen for humans, and is consequently limited to very small amounts in many grades of gasoline 

olefins content - In gasoline, olefins have tendency to form coatings on engine walls, reducing performance over time

TV/L - measure of gasoline volatility as the temperature at which volume of vapor is 20 times volume of liquid 

Gasoline blending

Gasoline is typically a complex blend of many different refinery intermediate streams. The most common refinery-produced components in the gasoline pool are:

FCC gasoline from the FCC unit - good octane and vapor pressure, but often high in sulfur and olefins.

reformate from the reformer - high octane and low vapor pressure, but high in aromatics

alkylate from the alkylation unit - good octane and vapor pressure with no aromatics, olefins or sulfur

isomerate from the isomerization unit - moderately good octane, low aromatics and low sulfur, but high vapor pressure

light straight run naphtha directly from the distillation tower - low octane and high vapor pressure

Gasoline also often contains non-refinery sourced blend components, either as octane enhancers or to satisfy a renewable fuels mandate. Typical non-refinery sourced blend stocks include:

Ethanol - high octane with no aromatics or sulfur, but high vapor pressure

MTBE - high octane, no aromatics or sulfur, and low vapor pressure, but limited by environmental concerns related to storage and leakage to water reservoirs in some areas.  It is banned across the US.

ETBE - high octane with no aromatics or sulfur, but high vapor pressure