Vienna: Oil exporting countries lowered slightly their world demand forecast for 2012 on Tuesday as ministers gathered in Vienna to discuss output levels amid tensions over Iran and slowing global growth.

The Organisation of Petroleum Exporting Countries (Opec) said in its monthly report that world oil demand next year would reach 88.87 million barrels per day (bpd), revising downwards its previous forecast of 89.01 million bpd.

Rafael Ramirez, Venezuela’s oil minister (C) speaks to the media at his hotel prior to the 160th Opec meeting in Vienna, Austria, 13 December 2011. Bloomberg

For 2011, demand remained virtually unchanged at 87.80 million bpd, compared to 87.81 million bpd in Opec’s last monthly report in November.

The organisation thus expected year-on-year demand to grow by 860,000 bpd this year -- from 86.93 million bpd in 2010 -- and by 1.07 million bpd next year.

Opec ministers were already gathering in Vienna ahead of a cartel meeting on Wednesday where they were due to decide whether to change production quotas in the face of heightened Iran tensions, higher Libyan output and a weak economic output.

While it maintained its global economic growth predictions for 2011 and 2012 at 3.6% in its report, the cartel noted that this was thanks to developing countries who were “helping to compensate for (the) shortfall" in the OECD group of developed countries.

The debt-hit eurozone “remains the centre of uncertainty," it said, while Japan and the United States had also seen a downward revision of growth for next year.

Looking ahead, Opec noted: “slowing economic growth and the uncertain outlook for the global economy in the coming year highlight increasing risks facing the oil market in 2012."