There are two kinds of energy: renewable energy and non renewable energy. Almost 85 per cent of world consumption of energy is from non-renewable resources. Renewable energy is collected from those resources that remain unaffected even after sacrificing their energy such as solar, wind, water, etc. These green energy sources are more common in developing world due to their one time investment. However, developed nations mainly depend on fossil fuels (petroleum, natural gas and coal) and nuclear power (fission and fusion). Non-renewable resources are those resources that once exhausted can never be returned to their original form.

Industrialized states are more prompt in utilizing fossil fuels to meet the needs of their industries. These fossil fuels are a result of those plants and animals that were partially decomposed and buried in the crest of earth millions of years ago due to environmental changes. These fuels have high content of carbon dioxide and can be feasibly used. Natural gas, coal and oil are the mostly consumed fossil fuels where oil shells and tar sands are not used so frequently.

• Coal: The most abundant form of fossil fuels having an estimated reserve of one trillion metric tons. Asia, Eastern Europe and United States are the places where coal is found in abundance. Coal is burned to acquire heat that is used to convert water into steam which runs the generators that in turn produce electricity.
  
  
• Oil: There are a lot of energy products that can be extracted after refining the liquid petroleum or crude oil such as heating oil, jet fuels, diesel, gasoline, etc.). More than 50 per cent of the total oil exists in Middle East, where limited reservoirs are also present in North America. A large part of discovered oil is already utilized where search of new reserves is going on (is not putting forth hopeful results). If the consumption of oil is not controlled today than the remaining oil of the world will be exhausted in nest 30 years.
  
  
• Natural Gas: The residue of oil recovery is natural gas. It is basically a mixture of gases, commonly methane (CH4), ethane (C2H5), propane (C3H8) and butane (C4H10). The gas does not contain sulphur and it makes the fuel cleanest. It is called LPG (Liquid Petroleum Gas) when propane and butane are detached. Its usage is gaining popularity because it is cheap and environment friendly. About 100 million metric tons of natural gas reserves are to date estimate which will last for approximately 100 years. Middle East and Europe are the biggest containers of natural gas.
  
  
• Oil Shale and Tar Sands: The utilization of these sources is least. Oil shale contains Kerogen that is a waxy substance of carbon. On heating to 490 degree centigrade the Kerogen can be vaporized and then condensed to get shale oil. Abundant energy is required to mine and process the oil shale. Its reserves are plenty estimated at three trillion barrels. The world’s requirement of oil for next 100 years can alone be satisfied by consuming these oil shale. Tar sand contains thick crude oil which can not be recovered by conventional oil mining procedures. Steam is used for this purpose to push and flow the oil swiftly. Canada has the largest reserve of tar sand and it alone can provide oil worldwide for about 15 years. These resources are not exploited mainly due to heavy cost of mining and environmental concerns.
  
• Nuclear Power: The procedure involves the fission of uranium particles to produce heat that can convert water into steam which later on produce electricity. Some of nuclear reactors are used in United States. It is clean source of non-renewable energy (no pollutants or green house gases) but involves threats of mishandling.

No doubt our planet is full of energy resources but it is our duty to exploit only those reserves that cannot cause harm to the environment. The constant consumption of fossil fuels has evolved threats of fuel extinction but we are provided with many alternates. Need of the hour is to invent not only cost effective but also environment friendly methods (to limit the hazardous residues) to fulfil the increasing demand of power.