Process for producing an additive concentrate having a viscosity of less than 1000 cSt at 100 EC, by reacting at elevated temperature and in the presence of an inorganic halide or calcium acetate catalyst (A) either (i) a hydrocarbyl phenol or (ii) a hydrocarbyl phenol and sulphur, (B) an alkaline earth metal base added in either a single addition or in a plurality of additions during the reaction, (C) either a polyhydric alcohol having from 2 to 4 carbon atoms, a di- or tri- C.sub.2 to C.sub.4 glycol, an alkylene glycol alkyl ether or a polyalkylene glycol alkyl ether, (D) a lubricating oil, (E) carbon dioxide added subsequent to the, or each, addition of compound (B), and (F) sufficient to provide from 12 to less than 40% by weight based on the weight of the concentrate of either (i) a carboxylic acid having the formula RCH(R')COOH, wherein R is a C.sub.10 to C.sub.24 alkyl or alkenyl group and R is either hydrogen, a C.sub.1 to C.sub.4 alkyl group or a --CH.sub.2 --COOH group, or an anhydride, acid chloride or ester thereof or (ii) a di- or polycarboxylic acid containing from 36 to 100 carbon atoms or an anhydride, acid chloride or ester thereof, the weight ratios of components (A) to (F) being such as to produce a concentrate having a TBN greater than 350.