Demand for oil will continue to grow slowly in 2011, when world economic expansion is projected to be slightly lower than this year's, OPEC said on Friday.

The Organization of the Petroleum Exporting Countries said: Given the current supply/demand outlook, the overhang in inventories is not expected to change significantly in the coming quarters.

In its Monthly Oil Report, OPEC left unchanged its forecast of a 1.05 million bpd increase in 2011 in global oil demand to 86.56 million bpd.

The group tweaked upwards its forecasts for global oil demand this year. Its current estimate of demand for 2010 is 85.50 million barrels per day (bpd) -- 1.05 million bpd higher than in 2009. The growth is 100,000 bpd higher than it had estimated in July.

OPEC's low estimates for 2011 oil demand growth by historical standards are based largely on its forecast that world gross domestic product growth will slow marginally to 3.7 percent next year from 3.9 percent this year.

The International Energy Agency forecast a 1.3 million bpd rise for 2011 in its own monthly report on Wednesday.

OPEC raised its estimate of demand for its own crude in 2010 to 28.74 million bpd. In 2011, the demand for OPEC crude is expected to average 28.92 million bpd, about 80,000 bpd higher than its previous assessment.

It estimated that supply from non-OPEC countries would total 51.92 million bpd this year -- an upward revision of 60,000 from its previous estimate. In 2011 it expected this to rise to 52.27 million bpd.

OPEC members' production has been creeping higher. Members with output quotas -- all except Iraq -- produced 26.861 million bpd in July according to the organization, 142,600 bpd more than in June. Including Iraq, production was 29.197 million bpd.

The organization's members met 52 percent of their targeted 4.2 million bpd cuts in July, down from 55 percent in June, according to Reuters calculations. based on OPEC data. The cuts were agreed in 2008.

(Reporting by David Turner and David Sheppard; editing by Jane Baird)