According to the Edexcel GCSE exam course book, we still have approximately 50 years left of oil on earth, but that is assuming that we do not find new supplies, which is quite likely. We have approximately the same supply of natural gas. However, our supply of coal is a lot larger and could last well over 1000 years. It is assumed that in the future, we will be able to use coal somehow as a substitute for oil, as both are fossil fuels. Of course, this is just prolonging the time when we will run out completely, as fossil fuels were formed over millions of years, and we are using them up at a much, much quicker rate. However, I would like to think that, given the time we do have before they run out, we will be able to develop the use of other energy sources that will provide for our needs. It looks as if, at the moment, the next feasible alternative that would provide enough energy for demand would be nuclear power. Of course, this has huge disadvantages also, relating to radioactive waste and nuclear disasters, such as the one that occurred at Chernobyl. Clearly, the best option is to develop renewable sources.