Public transport in crowded cities, in particular bus services play an essential role in the mobility of its citizenry. However, an efficient, reliable and safe bus system is still a distant dream of many cities. This paper uses a simulation approach to provide some insight into the "'actors that contribute to the service quality of a bus system. SAS Simulation Studio is used to model a city bus route. The simulation model consists of a bus depot, bus stops, terminal station and a bus route. Parameters used in the simulation include the number of buses serving the route, maximum bus capacity, inter departure time of buses, travel time between stops, number of passengers boarding and alighting. The simulation is applied to a real bus route in Kuala Lumpur city center and a sensitivity analysis is performed to evaluate how the different variables affect the service quality of the bus system.