Opec predicts it will lose some market share in the global oil market in 2015 as the United States' shale oil boom gathers pace.

Despite predictions that global demand for oil will rise next year, the Organisation of the Petroleum Exporting Countries said it expects demand for its exports to shrink to an average of 29.37 million barrels of oil per day, 310,000 lower than 2014.

If correct, it would mean the group's crude market share would fall to less than a third of the market at 32%, down from 35% in 2014.

A new report from the exporter group expects an upturn in supplies in 2015, more so if Libya, Iraq and Iran production are back online. A mixture of international sanctions and geopolitical turmoil across the three Opec members have restricted supply and buoyed oil prices.

"Even if next year's world economic growth turns out to be better than expected and crude oil demand outperforms expectations, Opec will have sufficient supply to provide to the market," the Opec report said.

The group predicted rising global demand in 2015 as worldwide economic growth gathers speed, increasing by a further 1.21 million barrels of oil per day.

The United States would be the major force behind the increased demand, consuming more of its own oil and reversing a four-year demand decline in rich nations.

Oil consumption has been falling in the majority of industrialised nations on the back of weak growth and green regulation but Opec expects that trend to turn around.

While US oil production is expected to grow by 7% to 13.12m barrels a day in 2015, some of the additional output will be used for domestic demand, such as motorists.

Opec's monthly report said that the Iraq crisis had hit its overall production for June, down 79,000 barrels a day to 29.7m daily average over the month.