Evaluation of combustion parameters such as ignition delay and combustion duration are very important in the design and development of reciprocating diesel engines. So far, there is no established and straight, forward method for the estimation of these parameters. In this paper first the available methods have been reviewed. Limitations of the direct method have been discussed. Effect of some operating variables like compression ratio, speed, load and injection advance on the combustion parameters have been studied. An easy and reliable approach has been suggested for the determination of start and end of combustion for a direct injection diesel engine, minimizing the personal judgment. Procedure for calculating the ignition delay and combustion duration based on the experimental study has been highlighted for the proposed method. The application of the first and second derivatives of pressure versus time for various operating conditions and the utility of the derivative methods for the determination of the combustion parameters for a low compression ratio C.I. engine has been examined. From the present study it has been concluded that second derivative of pressure with respect to time seems to be the most appropriate for determining the combustion parameters in diesel engines.