Low-rank coals from Mequinenza (type III-S) and Utrillas (type III) basins, characterized by high sulfur content, as well as type I-S oil shales from Ribesalbes were analyzed by thermogravimetry. Process kinetics was studied using the Friedman equation to interpret one point data – temperature of maximum generation of oil and gas (maximum on several experimental and simulated TG curves recorded at heating rates 5, 15 and 25 K ⋅min –1 , Tmax). These results are contrasted with those obtained by a method based on NLS (nonlinear least-squares) algorithms which derives kinetic parameters from a single TG curve recorded within a temperature interval nearby T. The final conclusion is that the reliability of kinetic parameters obtained from one point (Tmax) at several heating rates is low. On the other hand, the Friedman isoconversional method was used to elucidate the kinetic scheme which is derived from dependencies of apparent activation energy (E) on conversion level (α ). Analysis of kinetic data of pyrolysis of Mequinenza coal shows that in this case the dependence of activation energy on conversion level is characteristic of a reversible reaction followed by an irreversible one, whereas in the case of pyrolysis of Utrillas coal and Ribesalbes oil shales such dependence is characteristic of a reversible reaction.