> First of all, if the goal is to prevent instability OPEC is doing a terrible job.

I mentioned this upthread, the instability OPEC is trying to prevent is civil unrest from not being able to fund their social programs and governments. They need a price that puts them in the black and the rest of the world will pay. If it was a free market the fracking boom would still be raging and oil would be $30/bbl. Many gulf nations would fall apart if oil was at that price for a long period of time hence the price manipulation. (I'm not sure how they got the frackers to ease up, some say many of the frackers were bought out by OPEC members and their wells capped but that's just conspiracy afaik)