As Amazon spokeswoman Kelly Cheeseman told Reuters, the company doesn't intend to do away with UPS and Fedex -- at least not yet, anyway. "Our own delivery efforts are needed to supplement that capacity rather than replace it," Cheeseman said.

But that doesn't mean Amazon can't squeeze out another dollar in the process. The major shipping carriers have recently started charging by volume rather than weight, which Reuters attributes to more people buying things like toilet paper and diapers online rather than in stores. To counter the rising shipping prices, Amazon has started shipping large boxes of lightweight items itself and passing off the heavier and more dense packages to its legacy shipping partners. According to Reuters, Amazon's planes have been flying at nearly full capacity, but at less than half their capacity by weight -- meaning they're likely saving on fuel costs as well.

At the moment, Amazon only flies to about 10 different airports near its warehouses across the US, but it uses smaller hubs and avoids stopovers that could lead to delays. Those less-trafficked airfields also allow Amazon's flights to leave later each night -- another advantage when most online shoppers have a tendency to finally hit the checkout button in the evenings when they're home from work.