With the increased interest in multi-user systems with distributed decision making tasks, such as network centric warfare and free-flight air traffic control, the concept of Shared Situation Awareness (SSA) has become more important. SSA relates to the awareness that different operators have of the system state and the information needs of their team-mates, in order to coordinate their actions effectively. However, there are many different definitions of SSA in the literature and no generally agreed methodology for measuring it. Investigation to date has primarily been conducted through human-in-the-loop (HIL) experiments, which typically are costly and return only subjective results. Agent based modelling has been proposed as a partial solution, using software agents to take the place of humans in experiments. This paper describes the application of agent based modelling to a multi-user system: namely, the SCUDhunt game. The paper examines different ways of sharing information between operators, and their effect on team performance in cases with less than perfect information. Agent based modelling enables performance to be tested on a wide range of scenarios quickly and repeatedly and yields insights that would be difficult to achieve through HIL experiments alone.