BUZZ-Oil producers, energy services firms fall ahead of OPEC decision

** Shares (Frankfurt: DI6.F - news) of London-listed oil and gas producers and energy services companies down as Brent crude falls to a 4-year low ahead of OPEC's meeting in Vienna on Thursday.

** Oil majors Shell (LSE: RDSB.L - news) and BG Group Plc (LSE: BG.L - news) were down 1-2 pct and were among top losers on the FTSE-100 bluechip index. Peer BP Plc was down about 0.7 pct.

** Energy services firm Petrofac Ltd was the worst loser on the FTSE-100 index, trading down about 3 pct, while Weir Group Plc fell about 1 pct.

** Oil prices have fallen nearly a third since their highs in June this year as a supply glut was compounded by weakening demand.

** All eyes are on Vienna as the Ministers from the Organization of the Petroleum Exporting Countries (OPEC) meet to decide on slashing production.

** The ministers were unlikely to agree on a production cut, sources close to the cartel said.

** EnQuest Plc (LSE: ENQ.L - news) , Amec Foster Wheeler Plc (Other OTC: AMCBF - news) , Afren Plc (LSE: AFR.L - news) and Hunting Plc (LSE: HTG.L - news) were the biggest losers on the FTSE-250 midcap index, falling between 2 to 3 pct. Ophir Energy Plc (Other OTC: OPGYF - news) was down about 1 pct.

** The benchmark Brent crude futures was down $1.7 at $76 per barrel at 11:55 GMT. (abhiram.nandakumar.thomsonreuters.com@reuters.net)