Interrail is not the only website that offers reservations (the app only forwards to the website).

Please specify the trains (origin, destination, date, departure time) so people can suggest alternatives.

The trip I had in mind was:

Munich - Milan - Marseilles - Barcelona - Seville - Madrid - Lisbon - Porto

However, I am becoming aware that it is challenging to go from Madrid to Lisbon in one day due to there no longer being a night train so I am open to other options here.

Don’t know if I should have posted here but my planned trip was:

Munich - Milan - Marseilles - Barcelona - Seville - Madrid - Lisbon - Porto

However, I am not sure if I can do Madrid - Lisbon in one travel day as the night train no longer runs.

For getting to Portugal, see Seat61.

For the rest: please specify origin, destination, date and departure time per train if you'd like advice. I suspect some can be done online and others at the DB ticket office (or DB phone service) but we need details.

I guess my question is more general. Will I be able to reserve these trains before I arrive in Europe or will have to do so when I arrive. And secondly if I wait until I arrive, surely I am risking there not being any space left.

If you want something specific let’s say 18th May Marseilles to Barcelona, 08:02 - 12:34. It seems like the only option I have on the app is to reserve in person.

Reservations to Barcelona are only available on paper and can be done via:

• Deutsche Bahn: ticket office or +49 30 2970 (collect at DB ticket machine or via post for €5.90).
• SNCF: ticket office, maybe via phone (+33 1 84 94 3635, press #85 for English); not sure if they'll send tickets via the post.
• Interrail (+2€ booking fee and 9€ postage fee)

Pass holder seats for these trains are quota-controlled. Marseille - Barcelona is €19.

None of these will be free.

You can AVOID the faster and extrapay train from Mars to Barca by using local trains=means more changes. From Mil to Mars same-the slower route goes along coast via Nice and you can, but even that is not needed, use a It IC-train Mil-Genova-Ventimiglia.

For the superfast AVE trenes In ESpana-do that right after arrival in Barca at counter. DB should be able to do, but in practice it often hits unknowing staff. Someone has posted recently the ´magic code´ they have to use to even open their own system for this. CP in PT only locally.

The general fear so often reported here that trains are ´full/sold out´ monthes ahead is total nonsense.

@mcadv great answer thanks. One question is what does CP and PT mean?

CP is Comboios de Portugal, the train company in PT = Portugal.

I don’t know why mcadv writes so often abbreviations that are not common for everyone.

When making a reservation do I need my pass number?

That depends where you book.

Via Interrail: yes; if you bought your pass via Interrail though, the data should already be in your account.

Via SJ website or Belgian railways websites for TGV or Thalys/Eurostar: yes, you need a pass cover number, which is on the paper pass cover or which you can request here if you have a mobile pass.

Via DSB, ÖBB, DB, ČD: no number needed.