Whichever way you look at it if all the oil in the world suddenly came to an end then the modern world would too. We are still, sadly, totally reliant on it for so much. It still powers our power stations (although this is decreasing) we still rely on it to make our cars run (but electric is gathering a pace), it makes our waterproof clothing, (but, bamboo and old fashioned waxed cotton might offer an alternative) it is still engrained in our society. Without it Boilers Cheltenham, Gloucester, Swindon and Bristol would not function.
Oil comes from the ground. It is the result of millennia of geological pressures. The sites that produce oil were once under the sea. Sea plants and other organic matter, like Dinosaurs, sank to the bottom of the seabed where they were buried in mud. This mud became rocks and the heat from them warmed up the organic matter turning into Oil and Natural Gas.
There is also plastic to consider. Oil created this and it is even now becoming a real legacy issue. We as a planet have to stop relying on this substance, if not for the environmental benefits then for the solidity of our societies themselves.