The GNU General Public Licence is falling in popularity, looking at all the versions of the GPL as a whole, according to figures released on Tuesday by Black Duck.
At the same time, Microsoft's open-source software licence, MS-PL, is gaining ground in the open-source world, the company said.
Black Duck, which provides services and products for developers working with open-source code, compiled the figures from its database of more than 200,000 open-source projects collected from the internet.
The company found that the GPL was the most popular open-source licence, used by about 65 percent of the projects in the survey. In addition, it said that usage of the GPL v3 licence had expanded fourfold in the past year, from 2,345 in June 2008 to 9,500 in the current study.
Over the past year, the GPL v3 has moved past the Mozilla, MIT and Apache licences to the number-five spot, behind the BSD licence. Black Duck predicted that the GPL v3 would pass the BSD licence in about six months.
However, the GPL's share of overall licence-use dropped five percent, from about 70 percent a year ago to about 65 percent now.
Black Duck attributed the decline in the GPL's dominance to "pragmatism" on the part of software developers and users, who are increasingly moving to licences that place fewer restrictions on how the code may be used.
"Many developers are selecting licences that are less restrictive, a move that underscores the broader adoption and value of open source in today's multi-source development environments," Black Duck executive vice president Peter Vescuso, said in a statement.
The MS-PL has benefited from this trend to become the 10th most popular licence in Black Duck's database, used by 1.02 percent of all the projects in the study, the company said.
Most MS-PL projects are on Microsoft's CodePlex website and are oriented for Windows and .Net, it added.
Black Duck also noted that more software providers have moved to an "open-core" licensing model in the past year. Under this model, companies offer proprietary extensions around an open-source core, with examples including MySQL, PostgreSQL, and Continuent, Black Duck said.