Open source will start to dominate software infrastructure for providers of SaaS (Software as a Service) within three years. For them it's almost a no-brainer, according to Gartner analyst Yefim Natis.

"They will use it as much as possible," said Natis, vice president and distinguished analyst at Gartner.

Lower cost and better flexibility, compared to what's available from closed source, or proprietary software, are key factors for the growing popularity of open source in this segment of the market.

In order to compete with on-premise vendors, SaaS providers will have to offer a lower cost, and open source helps them do that, according Natis.

One big difference between most enterprises and large SaaS providers -- or cloud-based providers, as Gartner likes to call them -- is technical know-how.

The latter are often very technically advanced, which means they can run open source by themselves.

"Since they don't require support, it's really free" said Natis.

For SaaS providers the cost of its infrastructure is also very important, since it in turns decides the cost customers will have to pay.

To keep costs low they have to optimize infrastructure, and open source is the best option to do that, according to Natis.

But for open-source vendors, the SaaS trend isn't all good news.

In next couple of years SaaS providers will also challenge open-source vendors, and become the preferred method for lowering IT costs.

Both promise lower costs. But moving to a service model requires less IT skills, while a move to open source often demands the opposite, according to Gartner.