Originally Posted by
aviationwiz
Thanks for the good responses all. I always thought that the passport used when checking in should be the one used to enter the destination, though I see that's not always the case - or at least not required. Being a US passport is valid for my destination (just more costly in the form of visa on arrival), I'll check in with my US one and just provide immigrations on the other end with my other (South African) passport. Thanks!
And, for some countries where this is the case (i.e. Turkey), they already have your details, as you must have entered them in to get the evisa.