The thermochemical behavior of three raw and respective solvent extracted (ultrasound assisted) microalgae species CV (Chlorella vulgaris), SC (Scenedesmus obliquus) and NOc (Nannochloropsis oculata) - was studied in order to evaluate their potential as fuels. Thermograms were obtained for four heating rates (5-25 degrees C/min). The results reveals that (i) for all microalgae thermal degradation processes of carbohydrates, lipids and proteins were observed for temperatures below 450 degrees C, while the char oxidation occurred for temperatures between 450 and 600 degrees C; (ii) the raw CV and SC required less energy to initiate the oxidation process than the raw NOc due to the higher amounts of lipids present in the latter microalgae; (iii) the extracted SC and NOc showed a behavior significantly different than the raw SC and NOc in the stages related to the lipids and proteins decomposition; (iv) the FUR (Fourier transform infrared spectroscopy) spectra obtained for the raw and extracted microalgae showed significant differences in their oil and polysaccharides contents, revealing that ultrasound extraction using a mixture of n-hexane-isopropanol as solvent is adequate to extract these components from the microalgae studied; and (v) the calculated activation energy values are generally similar for the raw and extracted microalgae. (C) 2015 Elsevier Ltd. All rights reserved.