Members of the Organization of the Petroleum Exporting Countries at their regular meeting in June kept official oil production quotas set in 2008 in place despite dour economic forecasts regarding high energy prices.
Economists had worried high energy prices could trigger a double-dip recession. Market turmoil was exacerbated by Standard and Poor's decision to cut the U.S. credit rating to AA+ for the first time.
"Of course, we could not predict that the U.S. would be downgraded in the June meeting and it was a shock to OPEC when it happened," OPEC Secretary-General Abdallah el-Badri said in an interview with al-Arabiya.
The International Energy Agency shortly after OPEC's regular meeting ordered its members to release crude oil from emergency stockpiles to offset production declines from war-torn Libya, the 12th largest oil exporter in the world.
Badri said there was no way of knowing the future of Libyan oil production when OPEC met four months into the international conflict.
"OPEC did not know whether Libya's oil production would strengthen or weaken at the time of the meeting," he was quoted as saying.