A process for the production of a lubricating oil additive concentrate having a TBN greater than 300 which process comprises reacting at elevated temperaturecomponent (A) a defined mixture selected from defined sulphurized or non-sulphurized acids or calcium salts thereof,component (B) an alkaline earth metal base added either in a single addition or in a plurality of additions at intermediate points during the reaction,component (C) at least one compound which is (i) water, (ii) a polyhydric alcohol having 2 to 4 carbon atoms, (iii) a di- (C.sub.3 or C.sub.4) glycol, (iv) a tri-(C.sub.2 -C.sub.4) glycol, (v) a mono- or poly-alkylene glycol alkyl ether of the formula (I)R(OR.sup.1).sub.x OR.sup.2 (I)wherein R is a C.sub.1 to C.sub.6 alkyl group, R.sup.1 is an alkylene group, R.sup.2 is hydrogen or a C.sub.1 to C.sub.6 alkyl group and x is an integer from 1 to 6, (vi) a C.sub.1 to C.sub.20 monohydric alcohol, (vii) a C.sub.1 to C.sub.20 ketone, (viii) a C.sub.1 to C.sub.10 carboxylic acid ester, or (ix) a C.sub.1 to C.sub.20 ether,component (D) a lubricating oil,component (E) carbon dioxide added subsequent to the, or each, addition of component (B),component (F) a defined carboxylic acid or derivative,component (G) at least one compound which is (i) an inorganic halide or (ii) an ammonium alkanoate or a mono-, di-, tri- or tetra-alkyl ammonium formate or alkanoate provided that when component (G) is (ii), component (F) is not an acid chloride,the weight ratios of all components being such as to produce a concentrate having a TBN greater than 300.