Being part of Oneworld means that the airlines sell tickets for their own flights as well as for other members' flights (for example, British Airways sells tickets for American Airlines flights). This is good for the airlines because the customers can get their tickets in one place and it lets the airlines use flights that they wouldn't normally have. Also, Oneworld has a frequent flier program, where all the separate member airlines' airmiles can be used, so they can be used across all the member airlines. The three levels are Oneworld Ruby (lowest), Oneworld Sapphire (middle) and Oneworld Emerald (highest). It is up to the airlines to decide how many air miles a passenger needs to get rewards from their own scheme. A passenger is awarded one air mile for each mile that they fly with the airline for.