This paper describes an ongoing project with the goal of designing and implementing a method to evaluate visualizations based on the tasks supported. The method evaluates time to perform the task and the quality of the user solution. This method is described in detail in this paper. A software tool which uses visualization to support users performing environmental analysis was used to test the first version of this method. The software tool evaluated helps users to perform the computations of environmental impacts of two products. Two versions of the same software tool were used. The first version uses interactive tables and the second version displays the information using different types of interactive visualizations. The software tool was evaluated with users solving a task, which consists of selecting a product from two alternatives based on environmental parameters. The users were divided into two groups. Each group of users solved the same task but they were using different soft...