This graphic is from a New York Times article today in the Travel section. It shows the crazy game that exists for getting free upgrades. The way to make sure you sit in first class is to buy a first class ticket. However, if you are an elite member of the airline's frequent flyer program then you stand a chance of snagging that upgrade. This graphic uses Delta Air Lines as the example, but just about all legacy carriers (not Southwest) have similar structures to their programs. This is almost impossible to explain in a logical/linear fashion.