More barrels of oil on the global market in part because of Libya are keeping oil prices lower, the Organization of Petroleum Exporting Countries said.

OPEC said in its monthly market report for September crude oil production from the 12 members of the cartel increased by 231,000 barrels per day last month to average 30.35 million bpd.

Iraq and Saudi Arabia were the only two member states to post a decline in oil production since the last monthly market report. Libya, meanwhile, posted in the highest gains in terms of percent.

Libya in August produced an average 538,000 bpd, a 26.5 percent increase from July and more than twice what it produced in June.

"An agreement to open some Libyan ports and resume exports of crude made additional barrels available on the global market and applied downward pressure on light sweet crude oil prices," OPEC said in a report published Wednesday.

The Libyan government brokered a deal in April with eastern rebel leaders to re-open oil export terminals. An eight-month blockade from rebels seeking more autonomy for the region known as Cyrenaica had cut Libya's oil export potential dramatically.

Last week, Libya's National Oil Co. said production has topped the August level reported by OPEC to reach 700,000 bpd.