In message , Aglians
writes
Is there a difference between Oyster and pre pay (or oyster pre pay)?
Does exist an Oyster that allows to travel without paying in advance?
Sorry if this is a stupid question but I am italian so I don't know well
London transport system.
Thanks.

Generally there's nothing that allows you to travel without paying in
advance, except under special circumstances which would be dealt with by
the supervisor at the station concerned.

I don't think that's exactly what you meant though.
--
Kat Me, Ambivalent? Well, yes and no.