Hartsfield-Jackson International Airport is the world's biggest airline megahub, but it doesn't have the highest concentration by a single airline, according to a report.
Megahubs like Hartsfield-Jackson are usually dominated by a single carrier, said air travel data network company OAG in its report. Delta Air Lines has more flights out of Atlanta than any other carrier.
In Atlanta, Delta dominates more than 80 percent of the airport, including Delta Connection. But it's not the largest concentration by a single carrier. Other airports have an even higher portion of the market controlled by just one airline, with a smaller share going to other competitors.
Here's a rundown of some of the airports most heavily dominated by a single airline, according to OAG:
Charlotte: US Airways operates 88 percent of flights
Dallas-Fort Worth: American Airlines operates about 81 percent of flights
Atlanta: Delta operates about 80 percent of flights
Houston George Bush Intercontinental: United operates 76 percent of flights
Airline hubs benefit from economies of scale, by pooling together millions of passengers and hundreds of flights at a single meeting point to facilitate connections. That allows airlines to gather enough passengers from all over to fill each plane, even to smaller towns, or on overseas flights that require larger aircraft.
In Atlanta, as many as 570,000 possible connections are available in a single day, according to OAG.
But some other cities that have airports heavily dominated by a single airline also have competition in another form: A second airport.
Dallas has Love Field, dominated by Southwest Airlines. Houston has Houston Hobby airport, also dominated by Southwest.
Atlanta has no second commercial airport -- thought it has both Delta and Southwest operating at Hartsfield-Jackson. Meanwhile, Paulding County's airport has launched an attempt to commercialize, facing opposition from Delta, the city of Atlanta and some residents.