While in early years, software technology companies such as IBM and Novell invested time and resources in open source software (OSS) development, today even user firms (e.g., Samsung) invest in OSS development. Thus, today’s professional OSS projects receive contributions from hobbyists, universities, research centers, as well as software vendors and user firms. Theorists have referred to this kind of combined public and private investments in innovation creation as private-collective innovation. In particular, the private-collective innovation model seeks to explain why firms privately invest resources to create artifacts that share the characteristics of non-rivalry and non-excludability. The aim of this research is to investigate how different contributor groups associated with public and increasing private interests interact in an OSS development project. The results of the study show that the balance between private and collective contributors in the Linux kernel development seems to be changing to an open source project that is mostly developed jointly by private companies.