Delta and Virgin Atlantic announced the deal in December last year.

It involves setting up a joint venture allowing both carriers to offer more flights at Heathrow, Europe’s busiest airport.

The agreement is intended to boost Delta’s ability to better compete with industry leader United Continental and with American Airlines, whose partnership with British Airways dominates travel between the United States and London.

“The European Commission is likely to approve the deal without conditions,” said one of the sources, who declined to be identified because of the sensitivity of the matter.

A Commission spokeswoman declined to comment and there was no immediate response from Virgin Atlantic. The Commission is scheduled to decide on the deal by 20 June.

US regulators are also examining the deal.

Antitrust lawyers had said the authorities may be concerned about the reduced incentive for the two airlines to compete with each other once they set up the joint venture.

Delta is buying the Virgin stake from Singapore Airlines.