"Thank you for your email. I'm sorry for the delay in replying to
you.

You can top up your Oyster with the correct amount for a single
journey at any Oyster Ticket Stop or Tube station self service
machines. Below is a list of Oyster Ticket Stops.

http://ticketstoplocator.tfl.gov.uk/LocationLocator/

There is a minimum payment of £5 at Tube station ticket offices which
was introduced to prevent long queues for customers.


Please contact us if you need any further help.

Kind regardsi

Oyster Customer Services"

Will the self service machines take Us credit cards? if not do they
give change or is exact fare required?