OPEC oil output has fallen only slightly in June as increases in Iraq and Nigeria limited the impact of cutbacks by others, despite a wider OPEC+ deal and voluntary cuts by several members to support the market, a Reuters survey found on Friday.

The Organization of the Petroleum Exporting Countries has pumped 28.18 million barrels per day (bpd) this month, the survey found, down 50,000 bpd from May's revised figure.

The survey suggests little further progress by OPEC in limiting supply ahead of a further voluntary reduction by Saudi Arabia which takes effect in July, as part of the producers' latest agreement made in June to support the market.

The Reuters survey aims to track supply to the market. It is based on shipping data provided by external sources, Refinitiv Eikon flows data, information from companies that track flows such as Petro-Logistics and Kpler, and information provided by sources at oil companies, OPEC and consultants.

(Additional reporting by Ahmad Ghaddar; Editing by David Evans)