The UK airport empire of the former BAA company could be reduced to just one airport - Heathrow - by the end of the year.
Now known as Heathrow Airport Holdings (HAH), BAA once ran seven UK airports but now is responsible for just four - Heathrow, Southampton, Glasgow and Aberdeen.
HAH has now said that it was "entering a sales process" that could see Southampton, Glasgow and Aberdeen airports sold - possibly to HAH's biggest shareholder , Spanish transport infrastructure company Ferrovial.
In addition to its existing four airports, BAA - which used to be known as British Airports Authority - also once ran Gatwick, Stansted and Edinburgh airports.
But concerns about BAA's monopoly position and its performance at its airports led to an inquiry by the Competition Commission (CC) which is now the Competition and Markets Authority (CMA).
The CC ruled that BAA had to sell Gatwick, Stansted and one of either Glasgow or Edinburgh airports.
Global Infrastructure Partners (GIP) bought Gatwick in 2009 for £1.5 billion and Edinburgh in 2012 for £807 million, while last year Stansted was sold for £1.5 billion to the Manchester Airport Group.
A spokeswoman from HAH said: "Over recent months Heathrow Airport Holdings group shareholders and management have been considering their strategic position in relation to our three airports, Aberdeen, Glasgow and Southampton.
"As a result the group is now formally entering a sale process.
"Whilst there is currently no certainty that a sale will be concluded, the group intends to work towards completing a transaction by the end of the year."