A method of recovering humic acids from a material such as oxidised coal is provided. This method includes the steps of mixing the material with aqueous alkali, particularly aqueous sodium hydroxide, heating the mixture to a temperature above 100.degree. C. and below 180.degree. C. under sufficient pressure to prevent evaporation of the water, and maintaining the elevated temperature for a time, generally less than 2 hours, sufficient to extract a substantial amount of the available humic acids from the material.