They do not, but you will have to reactivate them if you do not use one
for 2 years.

"The money on your Oyster card never expires - it stays there until you
use it.
However, if your card is not used for 2 years, you will have to
reactivate it or
claim back any unused cash by calling the Oyster helpline on 0845 330
9876. "

http://www.tfl.gov.uk/tfl/fares-tick...user-guide.pdf

asdf wrote:

On Fri, 29 Dec 2006 10:18:05 -0000, tim..... wrote:

The cash on an Oyster card doesn't expire, strip cards usually
do (I've no idea about the dutch ones).

Oyster cards expire if you don't use them for 2 years.