If you have a balanced set of scales - and then you add just 5% on to one side - what happens? The scale quickly falls in favor of that side building momentum.
A macro market is no different - OPEC may only represent 40% (as you put it) but that is actually a huge number when they collectively make a decision.
You need to remember Russia is in on this deal as well once OPEC makes their decision so that adds another big oil producer.
And yes the contrarians are the one's buying into oil - not down ramping it - considering prior to the current OPEC decision there were more net shorts.
AKK Price at posting:
0.6¢ Sentiment: Buy Disclosure: Held