STOCKSHOTS: OPEC seen holding oil output to defend market share OPEC, keen to defend its market share against the US shale oil boom, is expected to hold output levels steady at its Vienna meeting this week, analysts say. The influential 12-nation Organization of the Petroleum Exporting Countries (OPEC), which pumps about 30 percent of the world's oil, will make the decision Friday at its semi-annual production meeting in the Austrian capital. FILES IMAGES OF OPEC BUILDING.