The behaviour of gasification process depends on different factors and parameters. Some factors do not have direct effect, but they affect other parameters, that have high influence on efficiency of gasification process. Equivalence ratio (ER), temperature in the reactor and fuel moisture content are three parameters which have dominant impact on the produced gas composition and gasification process in general. This study shows the literature review of works where effect of different factors on the gasification process is presented. The comparison and detailed analysis of collected study were done to determine effect of these three factors on the produced gas composition (CH4, H2, CO, CO2, N2). The last part of study presents mathematical description of the relationships between the most critical parameters and gasification process efficiency. Mathematical analysis is implemented using STATGRAPHICS Centurion software. Several discrepancies found in different studies are indicated and described in this article. It proves that analysed parameters have complex and mutual influence on the biomass gasification process. Description of the process allows finding theoretical optimum for every analysed factor. The results of this study can be used to develop a mathematical model of the gasification process and forecast the produced gas chemical composition.