Display omitted •Microwave-induced combustion was applied for light and heavy crude oils digestion.•It was feasible to determine all the REEs in heavy crude oil by ICP-MS.•Only diluted acid solutions were used in agreement to green chemistry recommendations. A procedure for light and heavy crude oils digestion by microwave-induced combustion (MIC) is proposed for the first time for further rare earth elements (REE) determination by inductively coupled plasma mass spectrometry (ICP-MS) equipped with an ultrasonic nebulizer (USN). Samples of crude oil (API density of 10.8–23.5, up to 250mg) were inserted in polycarbonate capsules and combusted using 20bar of oxygen and 50μL of 6molL−1 ammonium nitrate as igniter. Nitric acid solutions (1–14.4molL−1) were evaluated for analyte absorption and a reflux step was applied after combustion (5min of microwave irradiation at 1400W) in order to achieve better analyte recoveries. Accuracy was evaluated using a spiked sample and also by comparison of results obtained by microwave-assisted digestion combined to ultraviolet radiation (MW–UV) and by neutron activation analysis (NAA). Using 3molL−1 HNO3, quantitative recoveries (better than 97%) were obtained for all analytes. Blank values were always negligible. Agreement was higher than 96% for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y by comparison of results with those obtained by MW–UV and by NAA (only for La, Ce, Nd, Sm, and Yb). Residual carbon content in digests using MIC was always below 1%. As an advantage over conventional procedures for crude oil digestion, using MIC, it was possible to use diluted acid as absorbing solution, obtaining better limits of detection and avoiding interferences in REE determination by USN–ICP-MS.