The Oyster Card is a good way to save money on public transport in London because tickets for bus and Tube rides are considerably cheaper if they’re not bought individually. If you plan on using or needing a lot of rides in a 24 hour period, using the card means that transportation will never cost you more than a set amount. Oyster Cards can be bought at any Tube station for a £5 deposit as well as how much you want to put on the card. You fill up the card on the machine readers when you enter the Tube or bus and again when you exit. Once you’re done with it, you can cash it out at one of the machines and get your £5 back as well as any money that’s left on it.