For 4Q2017: “Amazon Web Services had 62 percent market share in the quarter, down from 68 percent a year earlier, KeyBanc’s Brent Bracelin and other analysts wrote in a note on Thursday. Microsoft Azure jumped from 16 percent to 20 percent, and Google’s share increased from 10 percent to 12 percent, they said.”
Original source: Amazon lost cloud market share to Microsoft in the fourth quarter: KeyBanc