A transmission fluid composition comprising: a major amount of a lubricating oil basestock; and a minor amount of an additive package comprising: (i) a mixture comprising two or more compounds of structures (I): where groups R 1 , R 2 and R 3 are independently alkyl groups having 1 to 18 carbon atoms or alkyl groups having 1 to 18 carbon atoms where the alkyl chain is interrupted by a thioether linkage, provided that, in the mixture (i), at least some of groups R 1 , R 2 and R 3 are alkyl groups having 1 to 18 carbon atoms where the alkyl chain is interrupted by a thioether linkage; (ii) one or more compounds of structures (II): R 4 -S-R 5 -O-R 7 R 4 -S-R 5 -O-R 6 -S-R 7 (II) where groups R 4 and R 7 are independently alkyl groups having 1 to 12 carbon atoms and R 5 and R 6 are independently alkyl linkages having 2 to 12 carbon atoms; (iii) one or more zinc dihydrocarbyl dithiophosphate compounds; and (iv) one or more oil-soluble or dispersible molybdenum-containing compounds, wherein the compounds of component (i) and component (ii) are each present in the composition in an amount from 0.1 to 2.0% by mass, based on the total mass of the composition; and wherein component (iii) is present in the composition in an amount from 0.4 to 5.0% by mass, based on the total mass of the composition. a major amount of a lubricating oil basestock; and a minor amount of an additive package comprising: (i) a mixture comprising two or more compounds of structures (I): (i) a mixture comprising two or more compounds of structures (I): where groups R 1 , R 2 and R 3 are independently alkyl groups having 1 to 18 carbon atoms or alkyl groups having 1 to 18 carbon atoms where the alkyl chain is interrupted by a thioether linkage, provided that, in the mixture (i), at least some of groups R 1 , R 2 and R 3 are alkyl groups having 1 to 18 carbon atoms where the alkyl chain is interrupted by a thioether linkage; (ii) one or more compounds of structures (II): R 4 -S-R 5 -O-R 7 R 4 -S-R 5 -O-R 6 -S-R 7 (II) where groups R 4 and R 7 are independently alkyl groups having 1 to 12 carbon atoms and R 5 and R 6 are independently alkyl linkages having 2 to 12 carbon atoms; (iii) one or more zinc dihydrocarbyl dithiophosphate compounds; and (iv) one or more oil-soluble or dispersible molybdenum-containing compounds, wherein the compounds of component (i) and component (ii) are each present in the composition in an amount from 0.1 to 2.0% by mass, based on the total mass of the composition; and wherein component (iii) is present in the composition in an amount from 0.4 to 5.0% by mass, based on the total mass of the composition. (ii) one or more compounds of structures (II): R 4 -S-R 5 -O-R 7 R 4 -S-R 5 -O-R 6 -S-R 7 (II) where groups R 4 and R 7 are independently alkyl groups having 1 to 12 carbon atoms and R 5 and R 6 are independently alkyl linkages having 2 to 12 carbon atoms; (iii) one or more zinc dihydrocarbyl dithiophosphate compounds; and (iv) one or more oil-soluble or dispersible molybdenum-containing compounds, wherein the compounds of component (i) and component (ii) are each present in the composition in an amount from 0.1 to 2.0% by mass, based on the total mass of the composition; and wherein component (iii) is present in the composition in an amount from 0.4 to 5.0% by mass, based on the total mass of the composition. <EOS>