No one knows how long it will last, but the international airfreight industry is partying like it's 1999.

Airfreight demand, measured in freight ton-kilometers, rose 12.7 percent in May compared with the same period in 2016, according to data released today by the International Air Transport Association (IATA), the global airline trade group. This was up from the 8.7-percent annual growth recorded in April, and is more than three times higher than the overall five-year average growth rate of 3.8 percent, according to IATA data.

Freight capacity, measured in available freight ton-kilometers (AFTKs), grew in May by 5.2 percent year over year. This continues a multi-month trend of demand exceeding supply, a recent reversal of what had been a persistent oversupply condition. The surge in demand bodes well for airfreight yields, which have been a problem for the past seven years.

In the five months that IATA's 2017 data has been available, demand has either been in the high single digits or in double digits. The weakest month so far has been January, when demand rose by 6.9 percent.

The strong performance this year may remind industry veterans of the halcyon days of the late 1990s, when the Internet and telecommunications build-outs, combined with the popularity of global just-in-time supply chain operations supported by air services, produced airfreight's last great period of success. The industry has been in a funk for the past 17 years, however, punctuated by short-term growth bursts that eventually fizzled.

Present-day demand growth is following the recovery in global economies, with the pace of new export orders nearing a six-year high in May. Industry executives expect demand to grow by 8 percent during the third quarter, IATA said.

Airlines in the Asia-Pacific region, the world's largest region for freight activity, reported a 11.3-percent rise in May volumes over the same period a year ago, while capacity rose 6.2 percent year over year, according to IATA data. Demand grew by 13 percent to 15 percent respectively on international routes within Asia and on Asia-to-Europe routes, IATA said. North American carriers posted a 13.9-percent volume increase year over year, while capacity rose by just 4.1 percent, IATA said. Seasonally adjusted volumes rose again in May after a jump in April, a sign of a lasting pick up, IATA said.

European airlines posted a 15-percent increase in freight volumes and a capacity increase of 5.7 percent, IATA said.