Different kinds of energy are used in different applications. For the most part, the fuels competing for use in electricity generation, in transportation fuels, and in heating and water heating, operating is almost completely segregated markets.
Mostly Electricity Generating Fuels
Several different fuels compete in the market for electricity production. Electricity in turn is used predominantly for lighting, cooking, and digital electric devices (computers, televisions, phones, etc.). It can be and is used for space heating and water heating but is far more costly than the alternatives. It is also used to power intracity trains and to power a very tiny percentage of automobiles that are plug in electric. (Hybrid vehicles, including many ships and submarines, use gasoline or diesel powered electricity generators in addition to directly using those petroleum based fuels.)
* "Thermal" coal is used almost exclusively to generate electricity (a small portion of coal is metallurgical coal is used to make "coke" which is used to make steel, and a small portion of coal output is used in other industrial processes as an energy source, as a filtration medium and as an ingredient for other chemical processes).
* Nuclear power and wind power and hydroelectric power are used almost exclusively to generate electricity. Historically, wind power was also used to pump water from wells and hydro power was used to operate small factories called mills to process grains and make textiles, but those applications largely ceased a century ago.
Today, hydropower is the predominant source of electricity in many developing countries. Nuclear power is used heavily in a number of advanced industrialized countries.
* Solar power (apart from passive solar design considerations in architecture which are usually considered an energy conservation design feature to reduce HVAC costs rather than a power source) is mostly used to generate electricity at the utility level, at the individual building level, and at the device level. Solar power is also used for water heating, both to pre-heat running hot water before it is further heated by other means, and to heat swimming pools.
Mostly Transportation Fuels
* Petroleum is predominantly used for transportation fuel (planes, trains, automobiles, submarines, boats, etc.). A small portion of petroleum is used for industrial processes. Heavy petroleum products also known as heating oil, is used for home heating in the Northeast and some very rural areas. Petroleum is used to generate electricity in Alaska, Hawaii and at local power generators used mostly as emergency back up power, in construction, and in other mobile applications (e.g. carnivals). Petroleum is also used as an lubricant, to make fertilizers and pesticides, and to make plastics.
* Biofuels are alcohols and diesel hydrocarbons made mostly from cooking waste and plant matter (e.g. corn and sawgrass) that are mostly used as petroleum substitutes in transportation applications.
Mostly Heating Fuels
* Natural gas is used widely for heating buildings and water in buildings, and for cooking. It is also used to meet peak electricity demands. It is also used in industrial applications as an energy source and as a chemical feedstock. There are also a modest number of vehicles (mostly fleet vehicles of businesses like United Parcel Service) that run on natural gas.