This study explored the effects of polyethylene terephthalate (PET) blending during the pyrolysis of oil shale (OS). Dynamic pyrolysis and co-pyrolysis tests at heating rates in the range from 5 to 40 degrees C/min were carried out using a thermogravimetric analyzer (TGA) coupled to a Fourier transform infrared spectrometer (FT-IR) to determine the kinetic parameters of the process and for online detection of evolved gasses. Pyrolytic decomposition of OS included a multi-stage decomposition process, while PET decomposed only in a single step. The kinetics of pyrolysis and co-pyrolysis was determined via model-free iso-conversional methods, namely Friedman, FWO, Starink, Vyazovkin, in a conversion degree range of 0.1-0.9. The kinetic models were validated with the obtained data to describe pyrolytic and co-pyrolytic degradation mechanisms, and the regression coefficients were between 0.9823 and 0.9999. The results showed that the activation energy of co-pyrolysis was evidently lower than that of PET or OS pyrolysis. This led to the conclusion that co-pyrolysis could be a potential method for obtaining shale oil due to the synergy between OS and PET.