A technical glitch has meant that passengers travelled for free in London today.
Transport for London's (TfL) Oyster card readers suffered a system fault.
Southeastern Railway tweeted: "We have been made aware of an issue with Oyster card readers across the network. TFL are working to fix the issues."
One user reported the card was not working on either buses or at tube stations and passengers at Morden, in south London, were being waved through ticket barriers by TfL staff.
Others highlighted the issue on social media.
Zora Suleman, from London, said: "Second time the Oyster card readers haven't worked. Hope there's a day-long glitch. Free travel for all."
And Sean Whitaker said "All Oyster card readers are out of service at Barking station. Staff are unhelpful and don't seem to bother."
The Oyster is a plastic smartcard which can be used for pay-as-you-travel fares as well as for travelcards, bus and tram passes. The card can be used to travel on bus, Tube, tram, Docklands Light Railway, London Overground, TfL Rail and most National Rail services in London.