A quaternary nitrogen-containing corrosion inhibitor of formula wherein is an aromatic, nitrogen-containing ring of 5 to 14 ring atoms, optionally containing an additional N, O or S ring atom and optionally substituted with one or more alkyl, alkenyl, aryl, arylalkyl, cycloalkyl, amino, aminoalkyl, alkoxy, hydroxylalkyl, or cyano groups, or a mixture thereof; Y is a group of formula —OC(O)R1 or —C(O)R1; L is C1-C10 alkyl, C2-C10 alkenyl or a group of formula —CH2CH(OR2)CH2—; R1 is C8-C20 alkyl or C8-C20 alkenyl; R2 is H or —C(O)R1; R3 and R4 are independently selected from H, alkyl, alkenyl, amino, alkoxy, hydroxylalkyl and cyano; and X is Br, Cl or I is particularly useful for inhibiting corrosion in oil and gas field applications.