Passengers can now buy Heathrow Express tickets for £5.50 each way if they book 90 days in advance.
Standard fares for Heathrow Express are £22 for a single per person and £36 return.
But the operator has recently introduced a raft of new cheaper deals for advance bookings.
"The fastest way to Heathrow from central London now costs less," says Fraser Brown, director of Heathrow Express.
"Since we launched our advanced purchase tickets in September last year it’s benefited a quarter of online customers. Now we want to encourage more people to book in advance and take advantage of our new prices."
Reduced fares are also available when booked 30 or 14 days in advance.
