Studies on open source software (OSS) have shown that the license under which an OSS is released has an impact on the success or failure of the software. In this paper, we model the relationship between an OSS developer's utility, the effort that goes into developing an OSS, his attitude towards the freedom to choose an OSS license, and the choice of OSS license. We find that the larger the effort to develop OSS, the more is the likelihood that the OSS license would be free from restrictions. Interestingly, the result holds even when all OSS developers prefer restrictive licenses or less-restrictive license. The results suggest that least-restrictive or non-copyleft license will dominate other types of OSS license when a large effort is required to develop derivative software. On the other hand, most-restrictive or strong-copyleft licenses will be the dominant license when minimal effort is required to develop the original OSS and the derivative software.