It's getting crowded up in the cloud.

While Amazon's (AMZN)  Amazon Web Services (AWS) maintained its lead in the cloud computing market in the fourth quarter, rivals such as Microsoft (MSFT) , IBM (IBM) , Alphabet  (GOOGL)  and Alibaba (BABA) are growing quickly -- in some cases, more quickly than AWS.

AWS revenue grew 45% to $5.1 billion in the fourth quarter, as it added customers such as Expedia (EXPE) , and Disney (DIS) and Time Warner's (TWX) Turner named AWS their preferred cloud provider. AWS is on pace to generate $20 billion a year in revenue, and has 34% of the cloud infrastructure services market according to Synergy Research Group. 

Microsoft said in its Wednesday earnings call that its Azure cloud service grew 98% in the quarter. Synergy puts the company's market share of the global cloud market at 13%, while noting that every company defines its cloud revenues differently.

"For example AWS revenue is predominantly (but not entirely) cloud infrastructure services," said Synergy Chief Analyst and Research Director John Dinsdale. "Microsoft includes in its cloud revenues a lot of SaaS and some professional services in addition to cloud infrastructure. IBM includes SaaS, professional services, hardware & software used to build clouds in addition to cloud infrastructure."

IBM Cloud, which contains diverse business related to cloud computing, posted a 30% gain in sales to $5.5 billion. The company's "as-a-service" division, however, which includes cloud computing and software-as-a-service revenues, grew 20% to $2.6 billion in sales and produces more than $10 billion on an annual basis. The business has 8% market share, according to Synergy

Google CEO Sundar Pichai said that his company's cloud business, which includes Google Cloud Platform and the G-Suite applications for businesses, are generating $1 billion per quarter during a Thursday earnings call. GCP is "the fastest-growing major public cloud provider in the world," Pichai added, without specifying its growth rate. GCP has 6% market share, Synergy says.

Meanwhile, Alibaba said that its cloud revenues gained 104% to $553 million on its Thursday earnings call. Alibaba Cloud has 4% market share, according to Synergy.

While Oracle (ORCL) did not make Synergy's top 5, its cloud platform and infrastructure as-a-service revenues grew 21% to $396 million in its most recent quarter, and software-as-a-service sales increased 55% to $1.1 billion.

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