Opec is expected on Friday to decide to slash production as the oil cartel faces its biggest test in more than a decade. But newly released data reveal that the cartel's vastly divergent economic circumstances will make the divided group's decision of how much to cut even more difficult.

PFC Energy, the Washington-based industry consultants, calculated that Opec countries need next year's oil prices to be anywhere from $10 to $100 to keep their import expenditures and export revenues in balance. The tiny nation of Qatar needs oil to be only $10 a barrel, while Iran requires $100. Saudi Arabia, Opec's most powerful member, needs oil to average $50 a barrel.