Network World’s analysis of publicly listed sponsors of 36 prominent open-source non-profits and foundations reveals that the lion’s share of financial support for open-source groups comes from a familiar set of names.

We found 673 companies on the donor rolls of our list of organizations – which was drawn heavily, though not entirely, from the Open Source Initiative’s list of affiliates.

Google was the biggest supporter of open-source organizations by our count, appearing on the sponsor lists of eight of the 36 groups we analyzed. Four companies – Canonical, SUSE, HP and VMware – supported five groups each, and seven others supported four. (Nokia, Oracle, Cisco, IBM, Dell, Intel and NEC.) For its part, Red Hat supports three groups – the Linux Foundation, Creative Commons and the Open Virtualization Alliance.

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It’s tough to get more than a general sense of how much money gets contributed to which foundations by which companies – suffice it to say, however, that the numbers aren’t large by the standards of the big contributors. According to Pro Publica’s non-profit records, the average annual revenue for the open-source organizations considered in our analysis was $4.36 million, and that number was skewed by the $27 million taken in by the Wikimedia Foundation (whose interests range far beyond open-source software development) and the $17 million posted by the Linux Foundation.

Split between, say, half a dozen companies, and even the Linux Foundation doesn’t look too hard to fund. What’s $2.83 million a year to Intel? The non-hypothetical, real-world price tag is actually lower, as it turns out – the foundation said that it charges $500,000 per year for platinum membership, $100,000 a year for gold, and anywhere from $5,000 to $50,000 for silver, depending on the size of the company.

It should be pointed out that this is still far from a complete picture – we used the most recent numbers available, but those were frequently from as long ago as 2011, and this doesn’t account for the many overseas groups and others not covered by the database – but it does suggest that, to a company like Google, even relatively major donations barely make a dent in the bottom line.

Another thing keeping the picture incomplete was a reluctance by some of the bigger companies to speak to us on the subject of their activities within the open-source community. We got only boilerplate responses back from two companies, and from list-topping Google, no response at all.

So what do they get out of it?

In the main, companies that support open-source nonprofits get brownie points – your developers can work on a project without the company joining an official foundation (and, importantly, vice versa), so the benefits of direct participation in a project aren’t necessarily related to the non-profit angle.

But those brownie points are far from valueless. All those services provided by non-profits are important to lots of people in the open-source community. Tejun Heo, a prominent kernel developer and Red Hat employee, gave the example of a hobbyist developer attending one of the many conferences on open-source held every year.

“A sponsoring company … would have a lot easier time getting acquainted with the person, and he or she would be a lot more likely to be familiar with and have a positive impression of the company,” he said.

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A lot of that goodwill, Heo added, has to do with the job market – sponsorship can make companies more attractive to potentially valuable developers, while keeping them in the loop on individual projects.

“Even if it doesn’t directly result in hiring, the wider contact surface ensures that Red Hat at least can stay in contact with what’s going on in terms of both technical and human resources aspects of the project,” he said.