Biofuels have raised controversy regarding their environmental, social, and economic sustainability. The complexity of biofuel decisions and investments by both industry and society requires integration of scientific knowledge, public information, and values from a diversity of sources. Environmental assessments can identify multiple impacts of different options. Open and collaborative knowledge creation can support decisions in two ways: by building trust and credibility and by developing more robust understanding of key issues. Open assessment is a decision-support method that allows widespread participation in a transparent and freely accessible process. In this article, we evaluate two open assessment case studies concerning biodiesel production. The evaluation compiles the participants’ views regarding the potential of the assessment process to influence decisions in terms of quality of content, applicability, efficiency, and openness. According to the evaluation, openness can be feasibly implemented and is much appreciated by participants. More experience using broad and active participation is needed for further development of methods and tools. However, the currently common practices of closed and disengaged processes limit decision making. In addition, suitable tools and practices, as well as the inclusion of participants with appropriate skills, are needed to facilitate open collaboration.