This research investigates the non-isothermal thermogravimetric analysis and kinetics of oil shale samples at different heating rates and in the air atmosphere. In all the oil shale samples studied, the TG-DTG curves indicated that the decomposition of oil shale samples followed two successive reaction stages in different temperature intervals, known as combustion and mineral decomposition. This stage determines reaction intervals, peak temperature, mass loss, and derivative mass loss rate values of oil shale samples. At the same time, the different combustibility indices such as the ignition index, combustion index, and reactivity of oil shale samples are also determined. Also, for each reaction region, activation energy values were calculated using four different model-free methods known as Kissinger—Akahira—Sunose, Ozawa—Flynn—Wall, starink, and distributed activation energy model. In combustion and mineral decomposition regions, the activation energy values varied between 122.9–162.5 kJ mol−1 and 169.9–264.2 kJ mol−1, respectively. At the same time, kinetic models were validated by comparing the experimental and simulated conversion curves.