Delta Air Lines is one of the world's largest airlines by traffic. Through its regional carriers (including subsidiary Comair), the company serves about 330 destinations in about 60 countries, and it operates a mainline fleet of 800-plus aircraft, as well as maintenance, repair, and overhaul (MRO) and cargo operations. The airline serves nearly 180 million customers each year and offers more than 15,000 daily flights. Delta is a founding member of the SkyTeam marketing and code-sharing alliance (airlines extend their networks by selling tickets on one another's flights), which includes carriers Air France, KLM, and Alitalia.