Fossil fuels are non renewable resource, that means once used they can not be replenished in the nature. However, fossil fuels are renewable but they take millions of years to revive. In this regard we can say that they are almost non renewable. Coal , petroleum and natural gas are fossil fuels which are used in industries and vehicles at a very fast rate, this will exhaust the reserves of these resources very soon and and after a decade or two we are required to find new sources of energy.