We propose an analytic method to evaluate groupware design. The method was inspired by GOMS, a well-known approach to analyze usability problems with single-user interfaces. GOMS has not yet been amply applied to evaluate groupware because of several fundamental distinctions between the single-user and multi-user contexts. The approach described in this paper overcomes such differences. We also illustrate the application of the model by applying it to the design of a collaborative tool for software engineering requirements negotiation.