Historical version 19 of Oyster Card (view current version)
Oyster Cards are the replacement for the old paper travelcards, for use on tubes, buses, Trams and overland trains in London.
They are contactless smartcards and do not need to be inserted into ticket machines, merely put close to a reader.
They can be used in many different ways, either as a sort of season ticket, or as a prepaid purse to buy tickets with. At the moment they are being issued to replace weekly, monthly and yearly travelcards of the old variety.
Routemaster conductors now carry little readers that will read your Oyster card. Other buses have a fixed reader next to the driver's seat. [Bendy Buses]? are different though - most bendy buses now have Oyster readers at all three doors so you can get on at any door.
As of early 2005, Oyster cards support daily capping. This means the most you will pay in a day is the cost of the appropriate day travelcard. (See this page). If you only use buses and trams, you will be charged £3 which is the price of a day bus pass.
A useful hint mentioned in the 2005 fares and tickets 2005 guide is that if your Oyster card contains only pre-pay (ie no travelcard) then any adult may use your card for pre-pay travel.
If you have a travelcard on your Oyster and travel out of your designated zones on the tube (and maybe mainline trains) then the gates will let you out, but you will not be able to use the card again until you put some prepay on it to cover the price of a zone extension ticket. This is a good reason to keep some prepay on your Oyster card even if you are a travelcard holder (see IvorW's comment below).
When being used on the tube you need to make sure that you touch the card to the reader at both ends of your journey (whether you are using prepay or a travelcard) so that the system knows how much to charge you. If you don't the system will guess an amount which will be more than you should have paid and in the case of a travelcard will probably guess that a zone extension is required.
You cannot yet use pre-pay on most overground train routes. The few exceptions are listed on page 23 (page 12 of the PDF) of the 2005 fares and tickets 2005 guide.
One of the benefits of buying a yearly travelcard (gold card) is that it gives discounts on some mainline trains (similar to the network card). However, as the oyster card shows no outward signs of what its validity is you need to carry around your receipt that you should have received when you bought the travelcard. For gold cards they are issuing special travelcard look-alike "Gold Record Cards" to use as proof. These record cards do not, however, act as a ticket, but merely as a shortcut to proof of your travelcard for those who do not have an oyster reader.
In theory you can top up you Oyster card or add a Travelcard online. But you then need to take it to the Underground station you have named (and until then you can't use it on a bus or National Rail or from a different underground station). In practice it may be simpler to use a Oyster Ticket Stop (mainly newsagents).
I bought one of these recently. I love it. Getting on buses is great, too, because there's no more need for the driver to squint at your ugly photocard picture and the expiry date on the travelcard. Whist buying it, I was warned strongly by the man in the office not to lose it, because the process for replacing a lost card is slow, tedious and annoying. I felt that was worth mentioning here. -- Earle
I'm very happy with mine. The one problem I've noticed is that, sometimes, I can go through a gate too close to the person in front, and you have to wait for the light on the reader to go orange before you try and open it. -- blech
A useful tip with Oyster cards that are travelcards, is to keep an amount of top-up in the card as well. This is useful for those occasional journeys outside the travelcard zones. I keep about 5 in it for the odd trip to Heathrow and the odd party happening in outer London. -- IvorW