Germany's Federal Cartel Office said Monday it has cleared the sale of utility E.ON AG's (EOAN.XE) gas transmission grid to a consortium led by Macquarie Group Ltd. (MQG.AU), a transaction worth 3.2 billion euros ($4 billion) that saw the Australian bank acquire its second German gas pipeline network in just over a year.

In a written statement the antitrust watchdog added, however, that it is separately investigating whether a possible cooperation between Macquarie's two gas pipeline grids could have constraining effects on competition in respect of capacity and grid fee calculations.

Macquarie's European Infrastructure Fund 4 and a group of international financial investors had agreed in the middle of May to jointly purchase E.ON's Open Grid Europe unit, which runs Germany's largest gas-transmission grid, a key asset in European gas trade due to its strategic location in the heart of the continent.

Macquarie had previously acquired Thyssengas GmbH, the former gas transmission grid operator of utility RWE AG (RWE.XE).

The cartel office said that both gas grids operate joint gas entry points, but have previously charged different grid fees, which prompted some customers to switch to the cheaper operator. It added that cooperation between the grids and a standardization of their grid fees could therefore have a negative impact on competition. In this case the cartel office could prohibit any cooperation or agree to concessions from Macquarie, a cartel office spokesman said.

He added, however, that there could also be positive implications from more cooperation between Maquarie's two gas grids, in which case no consequences should be expected.