oil/natural gas, for instance hydrogen sulfide and carbon dioxide. [0051] R1, R3 and R4 are preferably each independently an alkyl or alkenyl group of from 1 to 14 carbon atoms, in particular those groups having from 1 to 6 carbon atoms and especially methyl or butyl groups. [0052] Where R1 is C1- to C22-alkyl, C2- to C22-alkenyl, C6- to C30-aryl or C7- to C30-alkylaryl, counterions for the compo