OPEC (Organization of the Petroleum Exporting Countries) had 12 member countries for most of its history from 1967-2007 (Ecuador rejoined in 2007, Angola joined in 2007, bringing it to 13). The original 12 (1967-2007) were: Algeria, Angola (joined 2007), Ecuador (rejoined 2007), Gabon, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, UAE, and Venezuela. Given the era of this question, 12 is correct.