Interpretation of thermogravimetric analysis (TGA) data of organic materials usually faces difficulties for distinguishing the weight versus temperature data into a complex reaction scheme. This work proposed a general scheme to converting the TGA data into an Arrhenius-type kinetics that regarded the pre-exponential factor, the activated energy, and the reaction order as functions of conversion. The TGA data of two oily sludges were used as demonstrative examples. Agreement between obtained correlation with the experimental data was satisfactory.