This paper reports on a research to investigate the effectiveness of some commonly used monitoring systems, in detecting deviations from the planned cost and performance. The monitoring systems used in this work are: Leading parameter technique Variances method Activity based ratios technique The paper describes these monitoring systems; their characteristics, the measures they use and their effectiveness for assessing performance. The systems are first evaluated on a theoretical basis and then on the basis of results from investigations carried using simulation approach. A project model has been developed which realistically simulates the progress of the project and which generates information relevant to these monitoring systems. Factors affecting the project cost and performance are represented by changes in the project plan and inflation rates. It has been found that some of the earlier monitoring systems have more response to changes than the others. The research has also shown that the Activity based ratio’s technique gives a clearer and simpler indication of the overall progress of the project than the other two techniques.