Hi! Well, December is really high season. It really makes sense from December to mid-February to book ahead of time, especially for such touristy destinations such as Uyuni and Cusco, and if you are on some kind of schedule. Even if you do book ahead of time and then your plans change, we are in the position to change dates and even routes of your tickets, as long as the request comes with at least two workdays anticipation. So you can be safe and still maintain some flexibility. Cheers!

thanks for the detailed information.
I am planning to go to Uyuni from Cuzco in December. As I don’t have a definite date is it ok to book bus tickets on the spot? Do you believe i will have problems finding a seat etc. or i have to prebook ?

thanks