Kat wrote in
:

Clive wrote:
I've got an Oyster with pre-pay on it. Normally when I come to London
it is only for a day or two and therefore by paper after 9:30 travel
cards. This time I coming down on Friday for a week, can I get the same
sort on card put onto my Oyster for a week and how much will it cost
me. Thank you for any advice.

Yes, you can have a seven day travelcard put on your Oyster; the cost
will vary depending on the zones you want; it's £21.40 for Zones 1 and
2

Indeed if you buy at an Underground ticket office you may have no choice:
many are to be restricting the sale of paper 7 day tickets to busy times
(e.g. 07:00-10:00 Monday to Wednesday) or not selling them atall.