OPEC's clout has been declining for decades. The only time they put up a truly united front was the oil embargo of 1973. They are divided into different camps with different agendas.
Their share of the worlds oil market has been declining for decades and will continue to decline as the USA and Canada oil production continues to ramp up and as the Russian's continue to explore more of their vast untapped resources.
Most of the OPEC countries have a single resource--oil, they have no heavy industry of their own, depend on foreign nations for 90% of their arms industry, have backward social infrastructures, limited educational resources, and are plagued by conflicts, uprisings, civil wars, repression and unstable govts.
Anybody who bemoans OPEC's "world control" and "evil agenda" has some pathetic agenda of their own.