As the air cargo industry booms, the impact of new entrant Amazon.com Inc. (AMZN) - Get Report Prime Air remains a bit of a mystery -- obvious in some ways and hidden in others.

Of course, a 40-aircraft cargo airline operated by the world's fourth most valuable public company will influence the overnight cargo market, even if FedEx Corporation (FDX) - Get Report executives proclaimed in March that they are not worried.

"The evolution of e-commerce is transforming the global supply chain and creating significant new opportunities for Atlas," said Bill Flynn, CEO of Atlas Air Worldwide Holdings (AAWW) - Get Report , on the company's second quarter earnings call on Aug. 2. Atlas Air is one of two companies Amazon has selected to operate its fleet of Boeing 767-300 freighters.

"E-commerce is growing rapidly from low penetration levels," Flynn said. "It accounts for only about 6% to 7% of global retail sales, and much of that is streaming media. This create significant opportunities to expand globally."

Amazon said in January that it will build an air cargo hub at Cincinnati Kentucky International Airport in Hebron, KY, about 100 miles from Louisville, Ky., where United Parcel Service Inc. operates a hub. In terms of freight tonnage, the world's three largest airlines are FDX Express, Emirates Sky Cargo and UPS Airlines.

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Amazon Prime Air is still ramping up; hub operations began April 30. The fleet currently includes 16 Boeing 767-300s, according to website Planespotters.net. It will expand to 40 767s by 2018.

Some of the impact can be seen at airports such as Charlotte Douglas International Airport, one of a dozen destinations served by Prime Air. Year-to-date through May, the amount of express/overnight air freight at Charlotte Douglas, had gained 12% to 21,849 tons.

The increase reflects the impact of three daily flights by ABX Airlines, formerly Airborne Express: the flights serve Cincinnati and Allentown, Pa, both among the Prime Air dozen. At Cincinnati, in June, cargo volume rose 35% to 92,030 tons: at Lehigh Valley International Airport in Allentown, cargo volume through June was up 134%.

For investors, the Prime Air play so far has involved the two companies that lease cargo airplanes and crews to Prime Air. The companies, Air Transport Services Group (ATSG) - Get Report (which operates ABX Airlines) and, Atlas will each lease 20 Boeing 767-300Fs to Prime Air.

On Friday, shares in Air Transport Services Group closed at $22.70, up 42% year-to-date while shares in Atlas Air closed at $60.65 up 16%.

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Last week, on the ATSG earnings second quarter earnings call, Quint Turner, chief financial officer, said Amazon accounted for 42% of revenue, up from 22% in the same period a year earlier. Two ATSG carriers, ABX and Air Transport International, fly for Amazon.

Following the call, Cowen & Co. analyst Helane Becker raised her price target to $27. She has an outperform rating on the shares. "ATSG continues to grow its aircraft leasing business," Becker wrote in a recent report.

"Since ATSG is delivering the last of their 20-aircraft order to Amazon this week, future revenue growth will come mostly from adding new customers, increasing aircraft to existing customers or moving aircraft coming off lease to new customers at higher rates," she said.

During the Atlas Air call, Flynn said the company has "continued to move more deeply into the faster growing express and e-commerce markets."

More than 70% of the Atlas Air fleet operates in those markets, Flynn said, "and that percentage will increase as we ramp up from six aircraft for Amazon currently to an expected 20 by the end of next year."

Becker has a market perform and a $70 price target. "Atlas will benefit from robust air freight demand and leverage to growth in the e-commerce business," Becker wrote in an Aug. 3 report. "That said, we believe the shares {have} priced in a strong 2H17."

As for FedEx, CEO Fred Smith said he March earnings call that while Amazon is not a threat, executives want to be sure they avoid any disruption from its operations.

"Amazon is a wonderful company, and they certainly have revolutionized the e-commerce world, and we are not sure what Amazon is going to do one way or another," said Smith after an analyst questioned Prime Air's impact.

"The vast majority of FedEx business is business to business - 85% of our business," Smith said. "{That} has nothing to do with e-commerce.

"The FedEx system that consists of thousands of facilities, and the ability to pick up, transport, and deliver it, in one to two business days, between any two addresses in the United States, has been decades in the making," he said.

Smith said top FedEx executives "are putting a lot of effort into making sure that there is no opportunity for somebody to disrupt us on a substantial scale.

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.