petroleum generally refers to crude oil or the refined products obtained
from the processing of crude oil (gasoline, diesel fuel, heating oil,
etc.) We find petroleum products in every area of our lives. They are
easily recognized in the gasoline we use to fuel our cars and the
heating oil we use to warm our homes. Less obvious are the uses of
petroleum-based components of plastics, medicines, food items, and a
host of other products.
Gasoline is made from crude oil, which was formed
from the remains of tiny aquatic plants and animals that lived hundreds
of millions of years ago. These remains were
covered with layers of sediment, which over millions of years of extreme
pressure and high temperatures became the mix of liquid hydrocarbons (an
organic chemical compound of hydrogen and carbon) that we know as crude
oil. Because crude oil is made up of a mixture of hydrocarbons,
refineries break down these hydrocarbons into different products. These
"refined products" include gasoline, diesel fuel, heating oil, jet fuel,
liquefied petroleum gases, residual fuel oil, and many other products.
most basic refining process is aimed at separating the crude oil into
its various components. Crude oil is heated and put into a still -- a
distillation column -- and different hydrocarbon components boil off and
can be recovered as they condense at different temperatures. Additional
processing follows crude distillation, changing the molecular structure
of the input with chemical reactions, some through variations in heat
and pressure, some in the presence of a catalyst, a substance that
increases the rate of a chemical reaction without being consumed in the
The characteristics of the gasoline produced depend on the type of crude
oil that is used and the setup of the refinery at which it is produced.
Gasoline characteristics are also impacted by other ingredients that may
be blended into it, such as ethanol. The performance of the gasoline
must meet industry standards and environmental regulations that may
depend on location.
crude oil is refined into gasoline and other petroleum products, the
products must be distributed to consumers. The majority of gasoline is
shipped first by pipeline to storage terminals near consuming areas, and
then loaded into trucks for delivery to individual gas stations.
Gasoline and other products are sent through shared pipelines in
"batches." Since these batches are not physically separated in the
pipeline, some mixing or "commingling" of products occurs. This is why
the quality of the gasoline and other products must be tested as they
enter and leave the pipeline to make sure they meet appropriate
specifications. Whenever the product fails to meet local, state, or
federal product specifications, it must be removed and trucked back to a
refinery for further processing.
After shipment through the pipeline, gasoline is typically held in bulk
storage terminals that often service many companies. At these terminals
the gasoline is loaded into tanker trucks destined for various retail
gas stations. The tanks in these trucks, which can typically hold up to
10,000 gallons, usually have several compartments, enabling them to
transport different grades of gasoline or petroleum products. The truck
tank is where the special additive packages of gasoline retailers get
blended into the gasoline to differentiate one brand from another. In
some areas, ethanol may be "splash blended" in the tanker to meet
environmental requirements. When the tanker truck reaches a gas station,
the truck operator unloads each grade of gasoline into the appropriate
underground tanks at the station.
Note: Some resources in this section are provided by the
Energy Information Administration.