Train operators have agreed to introduce Oyster cards in London after accepting a £20m grant from the mayor.
Some 10m Oyster cards have been issued in London
Ten firms operating surface rail services into London will share the subsidy to install pay-as-you-go Oyster reading equipment.
The electronic cards are used across the city on the Tube, buses, trams and Docklands Light Railway network.
George Muir, of the Association of Train Operating Companies, hoped the scheme would be running by 2009.
Mr Muir said: "All London train operators will be responding positively to Transport for London's proposal for Oyster pay-as-you-go."
He said they wanted to enter into discussions with TfL to implement the scheme on railways in London as soon as possible.
Mr Muir added that further discussion was needed to reach agreement on the proper level of funding for different parts of the network.
Mayor of London Ken Livingstone said: "This is a step in the right direction, however there is some way to go before an agreement is reached.
"Transport for London will work with the companies over the next two months to try to resolve outstanding issues."
Train operators are also calling for progress in dual-reading gates at London's stations so they accept ITSO electronic cards.
The ITSO card, similar to the Oyster card, will be the standard smart card for railway passengers outside London.