Hydrocarbon materials are refined by solvent extraction with a mixture of liquid sulphur dioxide and boron trifluoride at a temperature below about 10 DEG C. and a pressure sufficient at least to maintain the liquid phase, the refined hydrocarbon materials forming the raffinate. In the case of aromatic hydrocarbon fractions such as crude benzols, toluols, xylols and naphthalene fractions, the process may effect desulphurization and decolorization. The process may also be applied to the refining of coal tar fractions such as distillates. Diluents and countersolvents such as liquefied propane, butanes, pentanes, hexanes or saturated naphthas, and co-solvents such as benzol, may be employed in the solvent extraction. The process of the invention may also be applied to the refining of aromatic and sulphur-containing hydrocarbon extracts obtained by the solvent extraction of hydrocarbon oils with organic solvents such as furfural, nitromethane, dimethyl formamide or methanol, or with inorganic solvents such as antimony trichloride, liquid hydrogen fluoride or liquid sulphur dioxide. In the treatment of hydrocarbon extracts obtained by solvent extraction with liquid sulphur dioxide, the extract may be partially freed of sulphur dioxide and then contacted with the boron trifluoride, in the presence, if desired, of a non-aromatic hydrocarbon as countersolvent. The process of the invention may be carried out in batch, continuous or semi-continuous operating cycles and in one or more stages. The raffinate of the process of the invention may, after removal of solvent, be subjected to subsequent refining treatments with sulphuric acid, selective solvents, alkali, clay, or water, or redistillation. Apparatus is described wherein the feedstock is dehydrated, deaerated, and diluted if necessary, and then subjected to the solvent extraction of the invention, the sulphur dioxide and boron trifluoride being recovered for recycle. Tests are described in which the process of the invention is compared with solvent extraction with a mixture of boron trifluoride with hexane or 3,4-dimethyl sulpholane.ALSO:Hydrocarbon materials are refined by solvent extraction with a mixture of liquid sulphur dioxide and boron trifluoride at a temperature below about 10 DEG C. and a pressure sufficient at least to maintain the liquid phase, the refined hydrocarbon materials forming the raffinate. In the case of petroleum hydrocarbons such as light naphtha fractions, gasolines, heavy naphthas, kerosenes, transformer oils, heater oils, furnace oils, Diesel fuels, gas oils, lubricating oils and crude oils, the process may effect the removal of sulphur, gums or other resinous materials, coloured impurities and odoriferous compounds, particularly mercaptans. In the refining of shale oil fractions, the process serves to remove oxygen compounds, nitrogen compounds and organic sulphur compounds. The process may also be applied to the refining of coal tar fractions such as distillates. Diluents and countersolvents such as liquefied propane, butanes, pentanes, hexanes or saturated naphthas, and co-solvents such as benzol, may be employed in the solvent extraction. The process of the invention may also be applied to the refining of aromatic and sulphur-containing hydrocarbon extracts obtained by the solvent extraction of hydrocarbon oils with organic solvents such as furfural, nitromethane, dimethyl formamide or methanol, or with inorganic solvents such as antimony trichloride, liquid hydrogen fluoride or liquid sulphur dioxide, or to the refining of sulphur-containing hydrocarbon raffinates obtained by solvent extraction with liquid sulphur dioxide. In the treatment of hydrocarbon extracts obtained by solvent extraction with liquid sulphur dioxide, the extract may be partially freed of sulphur dioxide and then contacted with the boron trifluoride, in the presence, if desired, of a non-aromatic hydrocarbon as countersolvent. The process of the invention may be carried out in batch, continuous or semi-continuous operating cycles and in one or more stages. The extract phase resulting from the process of the invention may be heated to recover all of the sulphur dioxide and much of the boron trifluoride, whereupon the residue separates into a second raffinate layer which may be recycled and which contains all the aromatic hydrocarbons in the original feedstock together with some sulphur compounds, and a second extract layer consisting mainly of an adduct of boron trifluoride with sulphur compounds. The adduct may be decomposed at a higher temperature to regenerate boron tri - fluoride. The first raffinate of the process of the invention may after removal of solvent, be subjected to subsequent refining treatments, for example treatments with sulphuric acid, selective solvents, alkali, clay, or water, or redistillation. Apparatus is described wherein the feedstock is dehydrated, de-aerated, and diluted, if necessary, and then subjected to the solvent extraction of the invention the sulphur dioxide and boron trifluoride being recovered for recycle. In examples, virgin heater oil, cracked cycle gas oil and cracked naphtha are refined according to the process of the invention. Tests are described in which the process of the invention is compared with solvent extraction with a mixture of boron trifluoride with hexane or 3, 4-dimethyl sulpholane.