Passengers touch it on an electronic reader when entering, and in some cases when leaving, the transport system in order to validate it, and where relevant, deduct funds from the stored credit.

It lasted until December 1995 and was a success, proving that it reduces boarding times, is easy to use, and is able to record entry and exit stops and calculate the corresponding fare fee, i.e. pay as you go.

However, the Upass smartcard of the South Korean capital Seoul was eventually the first in the world to roll out this sort of technology, at the end of 1995, eight years before London did as the "Oyster card".

MIFARE Classic chips, on which the original Oyster card was based, are hard-wired logic smartcards, meaning that they have limited computing power designed for a specific task.

Although the RFID chips were charged in the normal way and no fare evasion was involved, TfL disapproved of the practice and threatened to fine anyone not carrying a full undamaged card,[27] although it is not clear what the actual offence would be, were a case to be brought.

It can also be commenced at a London Underground station, an Oyster Ticket Stop (shop) or a Travel Information Centre; for this, the customer has to supply a security password and their postcode, which must then be cited when completing the registration online.

Visitor Oyster cards can be obtained from Visit Britain outlets around the world, and from other transport operators, such as EasyJet and Gatwick Express, and online and from any ticket office.

[40] In May 2006 TfL and the Department for Transport agreed a £20 million funding package for train operators to install the equipment necessary to accept PAYG at all London stations.

[43] A necessary precursor of the acceptance of Oyster PAYG was the introduction of zonal single fares on the National Rail network in London; this was implemented in January 2007.

London's trams operate on the same fare structure as buses; the rules are similar, and users with pre-pay must touch the Oyster card only once at the point of boarding.

Oyster photocards, with an image of the authorised user on the card front, are issued to members of groups eligible for free or discounted travel.

The cards are encoded to offer discounted fares and are available for students in full-time education (30% off season tickets), 16+ cards (half the adult-rate for single journeys on the Underground, London Overground, DLR and a limited number of National Rail services, discounted period Travelcards, free travel on buses and trams for students that live and attend full-time education in London) and for children under 16 years old (free travel on buses and trams and discounted single fares on the Underground, London Overground, DLR and most National Rail services).

Since 8 September 2006, students at some London universities have been able to apply for their 18+ Oyster photocard online by uploading a digital photograph and paying with a credit or debit card.

On 7 January 2008, Transport for London unveiled the Zip card, an Oyster photocard to be used by young people aged 18 years or under who qualify for free bus and tram travel within the capital, with effect from 1 June 2008.

[66] In 2005, Transport for London shortlisted two financial services suppliers, Barclaycard and American Express, to add e-money payment capability to the Oyster card.

[73] Oyster card holders (PAYG, Travelcard or Freedom Pass) receive discounts on the London Cable Car across the River Thames between Greenwich and the Royal Docks, which opened in June 2012.

Similarly, travelling via zone 1 is more expensive if a change onto the South Western Railway is made at London Waterloo compared to using the tube all the way from Euston via Earl's Court.

In return Transport for London agreed to open an office in the Venezuelan capital Caracas to offer expertise on town planning, tourism, public protection and environmental issues.

[73] In order to prevent "misuse" by a stated 2% of passengers, from 19 November 2006 pay as you go users are automatically charged the "maximum Oyster fare" for a journey on that network when they touch in.

Oyster users who do not touch in before making a journey may be liable to pay a penalty fare (£80) and/or reported for prosecution if caught by a revenue protection inspector.

As a consequence, some rail operators whose services run parallel to London Overground lines were forced to accept PAYG,[103] although only after some initial hesitation.

[97] The rollout was accompanied by the introduction of a new system of Oyster Extension Permits to allow travelcard holders to travel outside their designated zones on National Rail.

[9] TfL first started accepting contactless debit and credit cards on London Buses on 13 December 2012,[127] expanding to the Underground, Tram and the Docklands Light Railway in September 2014.

[132] In late 2017, TfL introduced the free Oyster card app which allows users to check their balance on a compatible Android or iOS smartphone.

Also, to celebrate 100 years of the Piccadilly line, a series of limited edition Oyster card wallets were commissioned from selected artists from the Thin Cities Platform for Art project.

Equally, if the barriers do not function (reading 'SEEK ASSISTANCE') and the TfL or train operating company staff member has to open the gates manually, then the maximum fare may be charged.

In her criticism of the figures, Pidgeon claimed that "structural problems" with the Oyster system were to blame, such as faulty equipment failing to register cards and difficulty in obtaining refunds.

[157][158] A report by BBC London highlighted the system of "autocomplete" (in which Oyster cards journeys are automatically completed without the need to physically touch out, exceptionally used when large crowds are exiting stations) as particularly problematic.

In late 2005 the Advertising Standards Authority ordered the withdrawal of one such poster which claimed that Oyster pay as you go was "more convenient" than Travelcards with "no need to plan in advance".

[180][181] The MIFARE chip manufacturers NXP Semiconductor sought a court injunction to prevent the publication of the details of this security breach, but this was overturned on appeal.