This isn't a completely exhaustive list, but it does include a lot of options traveling to different regions in different classes of service. (upgradedpoints.com)
«CheapOair has always been about getting the lowest price, but we also give you the option to upgrade into different classes of service and different types of ancillary products,» he explained. (rewardexpert.com)
Must an airline provide me with a seat in a different class of service to accommodate my disability? (transportation.gov)