Originally Posted by canadiancow

At the check-in counter? Near zero.

But if, at the check-in counter, you say (and I literally suggest quoting this) "I am on a business class ticket but only confirmed in premium economy, please add me to the business class onload list", you'll be pretty high up the list, as a passenger confirmed in premium economy. But this will result in you being upgraded (or not) at the gate, not at the check-in counter