In message , Tim Roll-Pickering
writes

I was in Barking today for the first time in ages and at the station every
single ticket machine I saw was noticeably not Oyster compatible. Yet isn't
Barking one of the stations were virtually all services accept PAYG, at
least in London?

Yes, and Barking is one of the NR stations that already sell Oyster
products, although not via ticket machines as yet.

And if I had found my balance running out on arrival, exactly where would I
be able to top it up at any time when services are still running?

From the ticket office (open 5.15 until 23.30) - or automatically from
the Oyster readers if you have auto top-up enabled, of course.

--
Paul Terry