OPEC is relevant because it does not work

OPEC is relevant to the world oil price. Its relevance comes from the breakdown between parties concerning any new production quotas. Iran with a coalition of other oil producers, Venezuela, Iraq, Angola, and Algeria have been unwilling to increase production in the face of higher prices. Its argument is that production is high enough and that a slowdown in growth could mean the world will have excess supply. Saudi Arabia wanted to have production increases and reduce the pressure on growth from prices above $100 / barrel.

The lack of an accord between OPEC members mean that unilateral action could be taken by countries which destroys any sense of a cartel. Note that production has generally been above quotas and the current gap is actually quite wide. The issue is not quotas as much as having production match the specific target of the group. This has generally not occurred. The real problem with an OPEC dispute is that it provide another backdrop of uncertainty about the dynamics of global oil supply.