How long until we run out of fossil fuels?
Fossil fuels are the fossilized remains of plants and animals and include coal, natural gas, petroleum, etc. These fuels are our primary fuels and primary sources of electrical energy (and heat), around the world. Industrial revolution and current living standards are many a times attributed to these fuels.
However, these fuels are running out. It takes millions of years for these fuels to form, whereas our rate of consumption of these fuels is much faster. Hence we are in danger of running out of fossil fuels. According to one economic theory, the price of fossil fuels will go up as the supply reduces and will ultimately reach a level where no one can afford it and hence there will always be some small quantity of fossil fuel left. Apart from that, there are some potential reserves of fossil fuels yet to be exploited and/or discovered. Rate of consumption of fossil fuels in several developing countries (Such as China and India) is increasing. Another relevant aspect is the emphasis on renewable energy sources, given the risks of global warming.
Thus, it is a very complex question and it is tough to state when these fuels will run out. However, if we assume that we will continue to use the fossil fuels at our current rate of consumption, there is a strong likelihood that we will run out of them by the end of this century or so. Thus, we do not (in most likelihood) have reserves of more than 1 century.
Hope this helps.