Atlanta Airport has retained its top spot in a list of the world's most efficient aviation hubs released recently.

Hartsfield-Jackson, the world's busiest international airport, came top in the annual Global Airport Benchmarking Report released July 8 by research group  the Air Transport Research Society (ATRS).

The report, which looks at everything from traffic figures, delays, management and passenger figures, named Atlanta, which is the hub of US carrier Delta, as the most efficient for the sixth year running.

Hong Kong also retained its crown as the most efficient airport in Asia, with Singapore in second place and Guangzhou in third place thanks to a boost of almost a third in efficiency from last year.

In Europe, last year's winner Oslo International had to share the top efficiency award with Copenhagen Kastrup, which ATRS attributed to a strong financial performance from Copenhagen.

The study also looked at the cost for airlines to operate (landing and passenger charges) in the world's airports, potentially providing some useful indicators of hubs that could grow quickly in the future.

In Asia, the lowest costs were to be found in Kuala Lumpur, said ATRS, along with Chennai and Mumbai in India - the highest were in Japan's Kansai, Nagoya and Narita airports.

In Europe, the charges were lowest at Brussels, Riga (Latvia) and Manchester (UK), while in the US they were lowest at Charlotte, NC, Atlanta, GA and Salt Lake City, UT.