Remember when upgrades were at the discretion of airline staff at the check-in counter? Frequent fliers were sometimes shifted “up front” when there were vacant seats. Passengers skilful in flattery, the snazzily dressed, or those adept at spinning a good sob story, might also elicit promotion.
Nowadays, things are a bit more equitable. Airlines discreetly reward their most loyal customers by occasionally bumping them up, but carriers now see unsold premium seats as ancillary revenue opportunities. So, in addition to paying a fixed amount with money or loyalty-scheme points, another option is to outbid fellow passengers in a pre-flight online seat auction.
The system powering the auctions comes from New York-based company Plusgrade, which lists 31 airlines (including Qantas, Lufthansa, Cathay Pacific, Air New Zealand, Virgin Atlantic and Etihad) as clients of its system, which is integrated into each airline's website.
There's a bit of variation between airlines, but if premium seats are available for auction the gist is: book as normal and you'll receive an email inviting you to bid, or an alert when you log in to your booking. You're presented with a suggested price range for your bid. You will see how much you're bidding and an indication of the strength of your bid. Auctions typically start at least 72 hours before a flight.
Bear in mind the following: find out the cost difference between the price of your ticket and the cost of a seat in the class you're bidding for. Don't make the lowest bid possible, but obviously it's pointless bidding the full cost of that difference. Anecdotal consensus is that around a third of that price difference is a good bet.
Chances for upgrade availability are improved when business travellers aren't flying, so booking flights that take off in the middle of the day might improve your chances.