Abstract: The present invention relates to a corrosion inhibitor for use in the oil and gas exploration, recovery and processing industries. In particular, the invention relates to a quaternary ammonium compound suitable for use as such a corrosion inhibitor, to the manufacture of the quaternary ammonium compound, to compositions containing it, and to methods of using it. Quaternary ammonium compounds of the invention have the formula (I) in which R is C1-6 alkyl, C2-6 alkenyl, aryl, aralkyl; X, Y, and Z are each independently hydrogen, or R1CO—, provided that at least one of X, Y and Z is R1CO, where R1 is C5-23 alkyl or alkenyl containing 0, 1, 2 or 3 double bonds; D is C2-6 alkylene; E is C2-4 alkylene; p, q and r are each, independently, integers from 0 to 20, with the proviso that p+q+r is from 3 to 20; and A? is an anion.