Express Bouricott does not usually accept walk-on passengers, so reservations are required ahead of time. Anyone who finds another pilgrim that would like to share the EB ride, please call or email EB for a reservation on that specific shuttle. On the date of your scheduled shuttle ride, you will likely have a full shuttle as it is a popular service, and I have never had to pay more than the minimum fare amount.
The three times I have used EB from Biarritz to SJPdP was quick and effortless. The driver will be inside the airport at the main door holding a sign. The drive is scenic, and it was enjoyable listening to the excited chit-chat of the other passengers.