One of the difficulties of using microalgae for the production of biofuels is the development of an efficient and economically feasible process for oil extraction from these unicellular organisms. Current methodologies involve toxic solvents (such as chloroform, benzene and methanol, among others), high energy requirements and high capital cost. The extraction processes using organic solvents in a Soxhlet apparatus with or without the assistance of ultrasound irradiation have shown promising results. In this context, the main objective of this study was to improve the oil yield of Acutodesmus obliquus using different mixtures of ethanol and hexane. Ethanol to hexane volume ratios of 1: 1, 2: 1 and 1: 2 (vol/vol) were used at 60 degrees C. The best extraction yield in relation to the total lipid content of the microalgae biomass was 92% for Soxhlet and 59% for ultrasonic irradiation using 1: 2 (vol/vol) ethanol: hexane for extraction times of 12 and 2 h, respectively. These extraction yields were significantly better than those of the pure solvents, i.e., 24% and 217% higher than ethanol and hexane via Soxhlet and 55% and 68% higher than the ultrasound-assisted extraction procedure. The ethanol to hexane volume ratio of 1: 2 (vol/vol) presented a superior performance in both Soxhlet and ultrasound-assisted extraction procedures by extracting a large amount of polar, non-polar and neutral lipids. Similar yields to the Soxhlet (12 h) with the ethanol: hexane 1: 2 (vol/vol) solvent mixture were obtained with ultrasound (for 40 min) followed by Soxhlet (4 h) extraction leading to a reduction of 164% in energy consumption.