Low-cost carriers, which emerged in the second half of the twentieth century following the global deregulation of the commercial aviation industry, operate relatively unique operating models. Once a relatively rare kind of airline to see operating, these kinds of carriers are ubiquitous today. There are a few characteristics shared by almost all low-cost carriers, and other features that are pretty much required for the operating model. Most low-cost airlines, for example, operate point-to-point services and avoid serving the highest-demand airports. Furthermore, they often pay their crewmembers less than most full-service airlines, and they find pretty much every way possible to lower operating expenses.