Germany's Federal Cartel Office Wednesday said an ongoing investigation into Germany's gasoline and diesel market has found the market is dominated by a few companies and further expansion of this oligopoly is unlikely to get antitrust approval.

The regulator said the oligopoly comprising the "vertically and horizontally integrated" players Total SA (TOT), Royal Dutch Shell PLC (RDSA.LN), BP PLC (BP), ConocoPhillips (COP) and ExxonMobil (XOM) already controls a a large part of the German gasoline and diesel market.

The strong concentration of the market represents a "meaningful obstacle" to competition, the cartel office added.

"On all market levels there are structures that strongly dampen overall competition," the cartel office said in a written statement.

Due to the current market structure a further expansion of the dominant companies through mergers and acquisitions will in future be very difficult or approved conditionally, the cartel office added.

As a first consequence of the gasoline and diesel market investigation the cartel office Wednesday decided to block plans by Total Deutschland GmbH, the German unit of Total SA (TOT), to acquire 59 filling stations from Austria's OMV AG (OMV.VI).

Total's plan to acquire the OMV filling stations would have given the oligopoly a market share of between 80% and 85% and would have eliminated OMV as "one of the strongest competitors," the cartel office said.

The cartel office further said it is still probing two other expansion projects Shell is pursuing.

Shell Deutschland Oil GmbH plans to acquire filling stations from the medium-sized companies Lomo and Honsel.

The deadline for the cartel office's decisions on these acquisition plans is June 9, it added.

Company Web site: www.bundeskartellamt.de

-By Jan Hromadko, Dow Jones Newswires; +49 69 29 725 503; jan.hromadko@dowjones.com