This paper summarizes the methodology and the main results of the comparison of the levels of service offered by public transportation systems in six Latin American cities: Santiago, Bogota, Guadalajara, Mexico City, Lima and Porto Alegre. The original contribution of this work is the design and implementation of a common methodology in all cities, ensuring that the comparison is correct. In turn, the method is flexible so as to adapt to the availability of information in each city. The core of the methodology is the selection of a representative sample of trips. For each of them, the level of service is estimated based on different variables such as speed, frequency, travel time, waiting time, etc., depending on additional information available about the system operation.