Worldwide every day,we devour the energy equivalent of about 200 million barrels of oil.Most of the energy on Earth comes from the Sun.In fact enough energy from the Sun hits the planets surface each minute to cover our needs for an entire year,we just need to find an efficient way to use it.So far the energy in oil has been cheaper and easier to get at.But as supplies dwindle,this will change,and we will need to cure our addiction to oil.　　Today petroleum,a mineral oil obtained from below the surface of the Earth and used to produce petrol,diesel oil and various other chemical substances,provides around 40% of the worlds energy needs,mostly fuelling automobiles.The US consumes n quarter of all oil,and generates a similar proportion of greenhouse gas emissions.　　Most experts predict we will exhaust easily accessible reserves within 50 years,though opinions and estimates vary.We could fast reach an energy crisis in the next few decades,when demand exceeds supply.As conventional reserves become more difficult to access,others such as oil shales and tar sands may be used instead.Petrol could also be obtained from coal.