Treatment of hydrocarbon streams, e.g. gasoline, with basic ionic liquids (ILs), results in reduction of the sulfur compounds such as H2S thiophenes, disulfides, thioethers, and/or mercaptans that are present to remove these compounds. The IL is a quaternary ammonium compound having the formula R4N+ X− or X− R3N+R′N+R3 X−, where R is independently an alkyl group, an alkylbenzyl group, a hydroxyalkyl group, or a hydroxyalkylbenzyl group, and R is straight or branched and has 1-22 carbon atoms, R′ is a straight or branched alkylene or oxyalkylene having 1 to 10 carbon atoms, and where X− can be hydroxide, carbonate, alkylcarbonate, bicarbonate or alkoxide, where the alkyl group of the alkylcarbonate or alkoxide, if present, is straight or branched and has 1 to 8 carbon atoms. The ILs can be used in applications where liquid or gaseous hydrocarbon fluids are treated by direct injection or by extraction.