A process for preparing branched alkyl aromatic hydrocarbons, which process comprises contacting branched olefins with an aromatic hydrocarbon under alkylating conditions, which branched olefins have been obtained by a process which comprises dehydrogenating an isoparaffinic composition over a suitable catalyst which isoparaffinic composition has been obtained by hydrocracking and hydroisomerization of a paraffinic wax and which isoparaffinic composition comprises paraffins having a carbon number in the range of from 7 to 35, of which paraffins at least a portion of the molecules is branched, the average number of branches per paraffin molecule being at least 0.5 and the branching comprising methyl and optionally ethyl branches; a process for preparing (branched-alkyl)arylsulfonates, comprising sulfonating branched alkyl aromatic hydrocarbons which branched alkyl aromatic hydrocarbons have been prepared by the said process for preparing branched alkyl aromatic hydrocarbons; and branched alkyl aromatic hydrocarbon compositions and (branched-alkyl)arylsulfonate compositions which are obtainable by the processes so defined.