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If you want a good debate, just ask a group of pundits about the size and profitability of Amazon(s amzn) Web Services then sit back with some popcorn. There are two main schools of thought: One holds that AWS is a business with razor-thin margins that is underwritten by the Amazon retail juggernaut and should that business take a tumble, AWS will fall with it. The other holds that Amazon makes good dough off of AWS, and that it could be a viable standalone business unit.

Count Macquarie Capital in the second camp. In a new research note, Macquarie estimates that the overall cloud market will hit $71 billion in 2015 and pegged AWS’ addressable part of that market at $38 billion. Those numbers are considerably larger than Gartner’s(s IT) previous estimates of $56 billion for the overall cloud market size and $28 billion for AWS’ piece of the pie. In the note, analyst Ben Schachter said AWS could now be worth $19 billion as a standalone entity, based on a 5X multiple of Macquarie’s 2013 AWS revenue estimate of $3.8 billion, or $30 billion using an 8X multiple.

Macquarie is betting that growing enterprise adoption — a key AWS priority — will feed that momentum. According to the report:

“We highlight that much of AWS?s past growth has come from SMBs [small and medium businesses] and start-ups. While these will continue to drive growth globally, in 2013 we expect a more concerted effort to focus on growing the AWS business at large enterprises. Importantly, the broadening platform offered by AWS is helping to drive adoption in larger enterprises (moving up the tech stack, with RedShift and other recent product launches). Additionally, we think emerging markets offer a significant opportunity, as many enterprises in these regions will likely bypass traditional technology infrastructure and go straight to the cloud.”

Redshift is the new data warehousing solution Amazon announced at AWS:Reinvent two months ago and that takes aim at expensive solutions from Hewlett-Packard(s hpq) (Vertica), Oracle(s orcl), SAP(s sap), and IBM(s ibm.)

Of course all of these estimates are based on analysis of numbers that Amazon doesn’t provide. The company lumps AWS revenue in with “other” revenue from marketing and promotion activities, other seller sites and co-branded credit cards. Given that, AWS remains pretty much a black box, but I would be willing to bet, all of Amazon CEO Jeff Bezos’ talk of low-margin, high-volume business aside, that Amazon is not doing cloud services as a philanthropic exercise.