Crude Oil is hydrocarbon and it is mixture of carbon and hydrogen.
It is knowen as Crude oil before it has been refined... Once it's been refined it can then be called gasoline, petrol, diesel and just "Oil"
because it is unprocessed and unrefined
U can doo it by fractional distillation...anyother questions i will be happy to help :)
Heavy crude is less in demand than light crude, because it needs more expensive refining to make it usable. Since it is less in demand, it is cheaper to buy.