Exit rows in PE

A couple of quick questions - are exit rows in PE only available at the airport or can they be chosen in advance? and either way is there an extra charge in the same way as in Y?

[Neil]

Only available to allocate at the airport and no charge apart from 28A/C on the LHR 747 IIRC

Wow, I didn't realise that the exit row seats were free on PE (on LGW config, say to Vegas). Will try to get those if I can in the future, I always assumed it was 100 quid added to return journey before...