This study reports the effect of differences in format of Prolog tracers on Prolog problem solving tasks. Three different tracers (Spy, T P M , and EPTB) in different formats were tested to check for their relative effectiveness in solving five different Prolog problems. 43 subjects attempted to solve each problem with each trace (15 problems in total). Preliminary analysis of solution times and response data indicate that E P T B performed best across all problems. An account for this finding is presented, as is one for a number of interesting interactions between the effects of problem type and trace format, which supports the general conclusion that while format is a significant determiner of access to information, it can also constrain the sorts of problems that could be solved readily with that information.