[wobbleblob]

I haven't done a quantitative study either, but here are two examples of extremely influential open source projects that the internet runs on:

The spring framework has contributions from many volunteers, but most big contributions and all of the integration work come from Pivotal.

The contributions to the linux kernel are graphed here:

https://www.extremetech.com/computing/175919-who-actually-de...

80% of new contributions are from companies. That shouldn't be surprising at all, because these companies are also the biggest users of the project.

As for myself, in the rare occasions I contributed a patch to an OSS project, most of the time it was to solve a problem I encountered at work, so I have anecdotal evidence that at least some from the category 'volunteers' also got paid to write that code.