Summary by @tldr:

But then the price started to moderate as western govts implemented policies to cut the amount of oil consumed.
Souce: Nasdaq What we see is speculation based on China's prospects (they were supposed to become voracious consumers of oil) until the 2008 financial crash brought some reality into the situation.
As a precaution Japan closed down all it's nuclear reactions till they checked them all for safety, and began to burn oil to generate their electricity.
There is a speculative hike from 2004 onwards as commodity traders convinced themselves that China was going to be the next thing and suck in a lot of iron ore and build a super economy and replace the USA.