Opec's share of the world market will shrink in 2014 as rising supply of US shale oil gives the exporter group little comfort from the fastest growth in world demand in four years.

The Organization of the Petroleum Exporting Countries forecast in a monthly report that demand for its oil in 2014 would average 29.61 million barrels per day (bpd), down 250,000 bpd from 2013, as an increase in supply outside the group outstrips an expansion in world demand.

The report points to a looming supply surplus next year should it keep pumping oil at present levels. The 12-member group has a target to produce 30 million bpd and in June, it produced 380,000 bpd more than the target.

"This would imply a further build in global crude inventories, which currently stand at high levels," Opec said in reference to the market outlook for next year. – Reuters