Right from the beginning the oil story has always been about big numbers. But what do those numbers mean?

Imagine a city building that is 1 kilometre square – about half the size of Sydney's CBD. Now picture it towering 4.5 kilometres into the sky, up amongst the clouds. That is the volume of oil that the world consumed in 2004.

Now imagine a new building being added beside it every single year, except each new building is 10 storeys higher than the one before.

By the time 2014 arrived, the new building was more than 700 metres higher - representing a massive 5.24 cubic kilometres of oil extracted and consumed - in one year alone.

That's how big the numbers get.

Still having trouble picturing it? You can "see" the building in this clip from Richard Smith's 2007 ABC documentary Crude - the incredible journey of oil.

Oil is a fossil fuel, formed by unusual geological circumstance over hundreds of millions of years from the remains of ancient phytoplankton.

The resource is most definitely limited, and some estimates suggest that in the past century the world has managed to consume half of all the oil there ever was.

Well before we run out of the stuff, we will reach what is called "peak oil" - the point at which oil production reaches a maximum before its inevitable decline.



The most optimistic market and industry voices still see the peak of oil production as far off in the future, if at all.

They point to growth coming from new technologies, unconventional deposits such as the tar sands in Canada, as well as new discoveries, but everyone accepts that the oil we've already used was the easiest and cheapest to extract.

New deposits are far more difficult to find and harness.



"With all its resources, its money and its incredible kit, the year that the oil industry discovered the most oil in one year that it ever will, was way back in 1965, and it's been kind of downhill ever since" Jeremy Leggitt - former oil geologist and now author - Half Gone: Oil, Gas, Hot Air and the Global Energy Crisis

Both OPEC and the International Energy Agency are projecting that the demand for oil will continue to increase and that the low prices the world is currently experiencing cannot be sustained beyond the short term.