Knowledge transfer is a critical factor in ensuring the success of offshore outsourcing software development projects and is, in many cases, neglected. Compared to in-house or co-located projects, however, such globally distributed projects feature far greater complexity. In addition to language barriers, factors such as cultural differences, time zone variance, distinct methods and practices, as well as unique equipment and infrastructure can all lead to problems that negatively impact knowledge transfer, and as a result, a project's overall success. In order to help minimise such risks to knowledge transfer, we conducted a research study based on expert interviews in six projects. Our study used German clients and focused on offshore outsourcing software development projects. We first identified known problems in knowledge transfer that can occur with offshore outsourcing projects. Then we collected best-practice solutions proven to overcome the types of problems described. Afterward, we conducted a follow-up study to evaluate our findings. In this subsequent stage, we presented our findings to a different group of experts in five projects and asked them to evaluate these solutions and recommendations in terms of our original goal, namely to find ways to minimise knowledge-transfer problems in offshore outsourcing software development projects. Thus, the result of our study is a catalog of evaluated solutions and associated recommendations mapped to the identified problem areas.