Oil macro analysis, page-32

Actually their goal is also to try to get the non-OPEC producers to join them in self regulating the prices, which is what OPEC has done in the past whenever prices dropped "too low". The problem they current face, and have for some time, has been that they've done what they've always done, which is to drop production, but the non-OPEC producers have continued to produce, thus taking a greater percentage of the market from OPEC. OPEC now really has no choice but to try to convince the non-OPEC producers that OPEC going alone in dropping production doesn't work, nor does everyone trying to continue to produce in the short term even if prices are below production for some, only to then find that that prices go crazy in the future due to the cutback in long term investment. Something has to change.

But even this is oversimplifying the situation.