British Airways owner IAG
The Commission, tasked with ensuring a level playing field in the 27-country European Union, did not provide details of the concessions, in line with its usual policy.
It extended the deadline for a decision on the deal to March 30 from March 16, the EU executive's website showed.
The bmi takeover would boost IAG's share of runway slots at London Heathrow airport to about 52 percent from 43.1 percent, allowing it to launch lucrative long-haul routes.
IAG also declined to give details of the concessions.
The European Commission typically requires airlines to cede slots and offer rivals access to their frequent flyer programmes in return for clearing mergers and acquisitions in the sector.
Lufthansa promised to offer slots to allow new entrants to operate flights on four routes singled out by the regulator, during its 2009 takeover of SN Brussels Airlines. Other concessions related to its code-share agreements and frequent flyer programmes.
Rival and failed bmi bidder Virgin Atlantic
(Reporting by Foo Yun Chee and Neil Maidment in London; editing by Rex Merrifield and David Hulmes)