Global Energy Systems Transition, (% of market)

Source: adapted from The Economist, February 10th 2001.

The usage of energy is in constant transition, particularly from a long term perspective. An energy transition is thus a change from one state to the other, namely in terms of supply, demand and quality. A common pattern in the energy transition involves moving to sources that have a higher energy content. In time, this has implied a growth of the quantity consumed, changes in energy sources and the usage of sources that tend to have a lower environmental impact. Even if there is a gradual transition away from petroleum, it still dominates global energy patterns. Several utility factors favor the usage of petroleum as the main source of energy in general, and for transport activities in particular:

Occurrence is the location of energy sources considering the demand. Several energy sources are only available when a transportation system that can support transfers between the supply and the demand exists. The exploitation of oil fields in several regions of the World (Middle East, Siberia, etc.) was made possible when an efficient transportation system based upon pipelines and tankers was established.
Transferability. The distance over which an energy source can be transported depends on its physical form (solid, liquid or gas), its energy content, and on the available transport technology. Most petroleum products are in a liquid, more or less viscous, form. They thus offer an efficient form to be transferred. Furthermore, economies of scale in transportation, notably maritime, enhance transferability.
Energy content. A low energy content is inadequate when demand is high and concentrated in space. Gasoline and other petroleum products have a high energy content compared to other fossil fuels like coal, but even more when compared to gravity (hydroelectricity) and solar energy.
Reliability. Continuous availability is an advantage over intermittent sources. The emergence of many sources and continuous supply through maritime and land routes has given a relative reliability for petroleum products. Some contemporary military interventions were performed to insure the reliability of oil sources and their transport.
Storability. An energy source has an advantage when it can be stored to answer variations in demands and interruptions of supplies. In liquid form, petroleum products are easily stored and several countries have built strategic reserves.
Flexibility is the capacity of an energy source to answer multiple usages. In addition to providing energy, petroleum by-products are the basis of whole industrial sectors (petrochemical) that synthesize goods like plastics, fertilizers, pharmaceutical products and synthetic rubber.
Safety. Sources that can be provided and used at low risks (human and environmental) are an advantage. Although the petrochemical industry presents some risks (accidents during extraction, refining, transport and usage), oil is considered a safe source of energy for its production and usage.
Cleanliness. Sources that produce few waste and are cleanly used are an advantage. Relative to other conventional energy sources like coal and wood and of the available technology, oil is cleaner to use and produces a limited amount of waste.
Price. Sources at low cost are generally preferred. Cost is often a function of the occurrence, the transferability and the energy content of the source. With massive investments on large scale extraction, refining and transport of petroleum products, a constant supply and intensive competition from several oil producing countries (although with some monopolistic control - OPEC), petroleum products prices are cheaper than many other sources.