In a free market "scarcity with a low price" is a contradiction. If there's scarcity the prices will be high, not low. And nobody's going to be reducing production if the prices are high.

> instability of oil production that OPEC tries to prevent

First of all, if the goal is to prevent instability OPEC is doing a terrible job. Secondly, a cartel is not needed to prevent price instability, as demonstrated by the hundreds of other commodity markets around the world which are not controlled by cartels engaging in price fixing schemes.

As with any cartel, the purpose of OPEC is to maximize profits for its members, artificially fixing the price of oil at a level higher than what it would otherwise be in a free market not controlled by a cartel. Price stability is a side effect of that, not the goal.

> 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)