Biodiesel is a nontoxic, sulfur-free and biodegradable petrol-fuel replacement that can be used in unmodified diesel engines pure or as a blend. Vegetable oils are the main feedstocks employed for its preparation but used vegetable oil and animal fats are currently considered one of the most attractive feedstocks for biodiesel production due to their lower market value in comparison with virgin oils alongside the fact that the material can be recycled from other industrial sectors. In this study, biodiesel-like biofuels are prepared from waste oils containing high concentrations of fatty acids, by using a family of acidic mesoporous carbonaceous materials denoted as starbon acids under both conventional heating and microwave irradiation. The solid acids are found to catalyze both the esterification of the free fatty acids in the waste oil with methanol and the transesterification of the triglycerides in the oil to give biodiesel and glycerol. starbonSO3H is found to be the most active catalyst under the investigated reaction conditions from a range of solid acids including zeolites and similar sulfonated carbonaceous materials. Conversions to fatty acid methyl esters were remarkably increased under microwave irradiation compared to the conventionally heated process.