FGW is perhaps the most interesting example of this happening, as they're
the least enmeshed with the Underground network of all the
north-of-the-river TOCs yet they accept Oyster PAYG on their routes
throughout the London zones. Sure, c2c and Chiltern accept it throughout the
zones as well these days - but their routes are very much entangled with the
Underground network.

By the by, the map of current Oyster PAYG acceptance on NR can be found here
(PDF):http://www.tfl.gov.uk/assets/downloa...on-nationa...- Hide quoted text -


While there isn't any FGW interavailability, the common gatelines at
Paddington, Ealing Broadway & Greenford would make it tricky to change
from the LUL PAYG rates.