On Jan 27, 8:10*pm, Roland Perry wrote:

In message , at 18:45:46 on Wed,
27 Jan 2010, Paul Terry remarked:

I know an OSI is an 'out of station interchange', but what's an OEP?

Oyster Extension Permit. Required only if you have a travelcard on
Oyster and want to travel beyond your zones on a National Rail service.

So it's basically the same as a BZx to station ticket then?

Yes and no - it's only available for travel *within* the zones (but
outside the zones covered by the season Travelcard).

The way it's been implemented is half-hearted at best - it's basically
a bit of an unworkable bodge (at present at least).