The battle for enterprise private cloud dollars is looking more and more like a battle between VMware's proprietary technology and open source cloud software OpenStack.

That is according to RighScale, a Santa Barbara, California-based vendor that helps companies choose and manage different kinds of cloud services. RightScale released the 2014 edition of its annual State of the Cloud report earlier this week.

About 30% of enterprises that responded to RightScale's latest survey said they viewed their VMware vSphere and vCenter environments as private cloud. While there were more respondents that said they were currently using VMware than OpenStack, the open source technology commanded more interest among survey participants.

“OpenStack is well-positioned to unseat VMware in private cloud – coming in first in interest and second in current usage,” RightScale said in a statement. While adoption of OpenStack grew between 2013 and 2014, adoption of vCloud director declined.

Microsoft's System Center had a “strong third position” among enterprises. Other popular private cloud technologies were Citrix CloudStack and Eucalyptus, coming in at fifth and sixth place respectively.

OpenStack is the leading open source cloud technology that is now supported by almost every major IT vendor. All major IT vendors also support VMware, as it provides the most widely used server virtualization platform.

VMware also has a fairly new cloud service offering, called vCloud Hybrid Service, which promises to seamlessly integrate internal enterprise IT environments virtualized on VMware with cloud resources deployed at VMware-managed data centers.

VMware unveiled the service in May of last year.

OpenStack is relatively young too. Taking root in Rackspace and the US National Aeronautics and Space Administration (NASA), the open source cloud development project only picked up steam, in terms of widespread industry support, over the past couple of years.

The report also ranked public infrastructure cloud providers, saying Amazon Web Services continued to dominate the market with interest in Google's Compute Engine and Microsoft's Azure growing. Between the two latter providers, Azure led among enterprises, while Google enjoyed more popularity among small and midsize companies.

Rackspace's public cloud service was second in the small and midsize company market.