Amadeus has signed a three year contents deal with BA which gives its agents access to the "full range" of the airline's fares.
It is the last major GDS to sign up with the UK carrier and the agreement ends months of negotiations between the twos sides.
The deal seems to be for similar terms on which the three other GDSs, Galileo, Sabre and Worldspan have signed up with BA.
Amadeus agents who join BA's opt-in scheme will be charged 50p per segment for BA premium class fares and £1 per segment booked on economy class fares.
Amadeus has now sent a letter to its UK and Ireland agents asking those who wish to join the opt-in scheme to confirm this in writing.
Tiffany Hall, BA's head of marketing and distribution, said: "We are delighted that we have signed a deal with Amadeus.
"This means that all four GDSs have now agreed to new contracts. This is good news for British Airways, the GDSs and the travel agents."
David Jones, executive vp commercial for Amadeus, said: "We recognise the crucial importance to our travel agency partners of delivering the most relevant travel content over a technologically advanced distribution platform.
"We are very pleased with this agreement which we believe takes into account the commercial priorities of both parties."
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