Related Clues:

• OPEC concern
• Cruet filler
• Drilling target
• Loosen, in a way
• Painter's medium
• Vein of ore
• Crankcase contents
• Heat source
• Glittering vein
• Certain cartel's concern
• Well-supplied resource?
• Barrel contents
• Peanut product
• Black gold
• Engine lubricant