In message , Dave Arquati
writes

I don't think you can go through the gate and pass your Oyster back to
other people to use it - the card expects an exit after an entry. You
can't do that with one-day travelcards either - there's some time delay
before being able to pass it through a gate again. However, like a
travelcard, you can give it to someone else *after* your journey has
finished.

I believe that is true if you have Pre-Pay (only) on the Oyster but not
if the Oyster also has a season ticket on it. I don't think you can give
a travelcard to someone else to use. According to the TfL "Conditions of
Carriage" ...

6.3 Use of tickets. Our tickets can only be used by the person
they were bought for. They must not be resold or given away for
further use. Doing this automatically cancels them and is an
offence under our Byelaws and the Public Service Vehicle
(Conduct of Drivers, Inspectors, Conductors and Passengers)
Regulations 1990. This rule does not apply to Carnet or bus
‘Saver’ tickets.
--
Paul Terry