Possible Clues:

• Cartel formed in 1960
• Cartel that added Angola in 2007
• Org. that creates output ceilings
• Group whose O doesn't stand for 'oil'
• Crude cartel?
• "Black gold" bloc
• Ecuador and Venezuela are in it
• Well-funded grp.?
• Grp. that has energy users over a barrel?
• "Black gold" gp