Petroleum (from Latin petrus -
rock and oleum - oil), mineral oil, or crude oil, sometimes
colloquially called black gold, is a thick, dark brown or
greenish flammable liquid, which exists in the upper strata of
some areas of the Earth's crust. It consists of a complex
mixture of various hydrocarbons, largely of the alkane series,
but may vary much in appearance, composition, and purity.
Petroleum has been known throughout
historical time. The first oil wells were drilled in China in
the 4th century or earlier. The oil was burned to evaporate
brine and produce salt. By the 10th century, extensive bamboo
pipelines connected oil wells with salt springs.
It was used in mortar, for coating walls and
boat hulls, and as a fire weapon in defensive warfare. Native
Americans used it in magic and medicine and in making paints.
Pioneers bought it from the Native Americans for medicinal use
and called it Seneca oil and Genesee oil. In Europe it was
scooped from streams or holes in the ground, and in the early
19th cent. small quantities were made from shale. In 1815
several streets in Prague were lighted with petroleum lamps.
The petroleum industry began with Edwin Drake's discovery of
oil in 1859, near Titusville, Pennsylvania. The industry grew
slowly in the 1800s and did not become a real national concern
until the early part of the 20th century; the introduction of
the internal combustion engine provided a demand that has
largely sustained the industry to this day. Early "local"
finds like those in Pennsylvania and Ontario were quickly
exhausted, leading to "oil booms" in Texas, Oklahoma, and
California. Other countries had sizable oil reserves as a part
of their colonial holdings, and started to develop them at an
While even in 1955 coal was
still the world's foremost fuel, oil began to take over.
Following the 1973 energy crisis and the 1979 energy crisis
there was significant media coverage of oil supply levels.
This brought to light the concern that oil is a limited
resource that we will eventually run out of, at least as an
economically viable energy source. At the time, the most
common and popular predictions were always quite dire, and
when they did not come true, many dismissed all such
discussion. The future of petroleum as a fuel remains somewhat
controversial. USA Today news (2004) reports that there is 40
years of petroleum left in the ground. Some would argue that
because the total amount of petroleum is finite, the dire
predictions of the 1970s have merely been postponed. Others
argue that technology will continue to allow for the
production of cheap hydrocarbons and that the earth has vast
sources of unconventional petroleum reserves in the form of
tar sands, bitumen fields, oil shale, and methyl hydrate that
will allow for petroleum use to continue for an extremely long
period in the future.
Today about 90% of fuel needs
are met by oil. Petroleum's worth as a portable, dense energy
source powering the vast majority of vehicles and as the base
of many industrial chemicals makes it one of the world's most
important commodities. Access to it was a major factor in
several military conflicts, including World War II and the
Gulf War. About 80% of the world's readily accessible reserves
are located in the Middle East. The US has less than 3%.
The presence of the oil industry
has significant social and environmental impacts, from
accidents and from routine activities such as seismic
exploration, drilling, and generation of polluting wastes. Oil
extraction is costly and often environmentally damaging.
Offshore exploration and extraction of oil disturbs the
surrounding marine environment. Extraction may involve
dredging, which stirs up the sea bed, killing the sea plants
that marine creatures need to survive. Crude oil and refined
fuel spills from tanker ship accidents have damaged fragile
ecosystems in Alaska, the Galapagos Islands, Spain, and many
other places. Renewable energy source alternatives do exist,
although the degree to which they can replace petroleum and
the possible environmental damage they may cause is
Most geologists view crude oil, like coal and natural gas, as
the product of compression of ancient vegetation over
geological timescales. According to this theory, it was formed
from the decayed remains of prehistoric marine animals and
terrestrial plants. Over many centuries this organic matter,
mixed with mud, was buried under thick sedimentary layers of
material. The resulting high levels of heat and pressure
caused the remains to metamorphose, first into a waxy material
known as kerogen, and then into liquid and gaseous
hydrocarbons. These then moved through adjacent rock layers
until they became trapped underground in porous rocks called
reservoirs, forming an oil field, from which the liquid can be
extracted by drilling and pumping.
Thomas Gold was the most widely known Western proponent of the
Russian-Ukrainian theory of abiogenic petroleum origin. This
theory suggests that large amounts of carbon exist naturally
in the planet, some in the form of hydrocarbons. Hydrocarbons
are lighter than rocks so they seep upward. Deep microbial
life convert them into the various hydrocarbon deposits.
There is also a new theory, presented in Scientific American
in 2003, which proposes that hydrocarbons are generated by
active nuclear activity in the Earth's core.
As of 2004, these theories are very much minority positions in
the community of geologists.