As mentioned above, I can only speak for U.S. passports and am not sure what the protocol is for other countries. But if you’re a U.S. passport holder and find yourself out of visa space while abroad, just head to the nearest Consulate or Embassy and have them insert a refill book. There’s a $82 fee (a small price you pay for being an avid traveler!), and you can do it up to two times, granted that your passport is still in relatively good condition (not ripped or mangled). I’ve had to do this twice now, and both times, the processes have been quick, easy, and painless. Just check on the Embassy/Consulate’s website to see if they require appointments or not; most do. If you’re in the U.S., you can send in your passport along with a DS-4085 form, and it usually takes 2 weeks to process. Also, if you’re applying for a new passport book and already know that you’ll need additional pages, you can request it at the time of application.