Seven common methods based on in-cylinder data, usually applied to determine the combustion parameters (ignition delay and combustion duration), are compared using in-cylinder data provided from a natural gas spark ignition engine operating under lean conditions. The influence of three engine operating parameters: spark advance, throttle opening and fuel/air equivalence ratio, on combustion parameters are tested using every method and the results are compared. The application of these methods on average and individual cycles is also performed. The advantages and disadvantages of these methods are presented and discussed. Some methods can be used. only for the ignition delay determination. A comparison with a motor-cycle, so a specific experimental device, is necessary for three methods. Others are very sensitive to noise, or can be used only in some restricted area of engine operating conditions. One method needs calculations based on several experimental assumptions. © 2005 Elsevier Ltd. All rights reserved.