ALGIERS (Reuters) - A number of energy ministers from OPEC oil-producing countries are likely to meet informally in Doha on Friday to try to build consensus over decisions taken by the full group in September in Algiers, an Algerian energy source said.

At the September meeting, OPEC agreed on modest, preliminary, oil output cuts in the first such deal since 2008, with special conditions given to Libya, Nigeria and Iran, whose output has been hit by wars and sanctions.

Doha this week is hosting a meeting of the Gas Exporting Countries Forum (GECF). Industry sources said on Tuesday that the Saudi Arabian and Russian energy ministers might meet on the sidelines of the forum.

The GECF unites 12 countries including Russia and OPEC members Algeria and Iran. Saudi Arabia is not a member but Energy Minister Khalid al-Falih was due to travel to Doha this week for meetings with peers.

The agreement made in Algiers is expected to be finalised at the next meeting of the Organization of the Petroleum Exporting Countries on Nov. 30 in Vienna, but disagreements persist among OPEC members and non-OPEC Russia on the details of the deal.

Iran, which remains one of the main stumbling blocks to a final deal, has refused to cap production below 4 million barrels per day as it seeks to regain market share lost under sanctions.

Russia has said it prefers to freeze output while OPEC wants Moscow to contribute to cuts.

(Reporting by Lamine Chikhi; Writing by Aidan Lewis; Editing by Patrick Markey and Dale Hudson)