A process to produce olefinic products suitable for use as or conversion to oilfield hydrocarbons from an olefins-containing Fischer-Tropsch condensate that also includes paraffins, where said olefinic products include a first olefinic product that includes branched internal olefins, a second olefinic product, and a third olefinic product that includes internal olefins, with the first olefinic product and the second olefinic product being such that a combination of the first olefinic product and the second olefinic product provides an olefinic product with at least 50% by mass of hydrocarbons having carbon chain lengths of between 15 and 30 carbon atoms per molecule, the process being characterised in that it includes the steps of: separating said olefins-containing Fischer-Tropsch condensate into a light fraction which is a C 5 -C 7 fraction, an intermediate fraction which is a C 8 -C 15 fraction which includes paraffins and alpha-olefins and a heavy fraction which is a C 16 -C 22 fraction which includes paraffins and alpha-olefins; producing said first olefinic product that includes branched internal olefins by oligomerising at least a portion of the light fraction using a zeolitic catalyst under an oligomerisation pressure of less than 15 bar and with an average catalyst activity chosen to inhibit cyclo-paraffin and aromatic production and to promote production of branched internal olefins; carrying out either one or both of the steps (i) and (ii) of: (i) producing said second olefinic product (a) by dehydrogenating at least a portion of the intermediate fraction to convert paraffins to internal olefins and producing an intermediate product which includes internal olefins and alpha-olefins, and then (b) by synthesising higher olefins, by means of dimerisation or olefin metathesis, from the intermediate product which includes internal olefins and alpha-olefins and optionally first separating the alpha olefins from the paraffins of the intermediate fraction before (a); and (ii) producing said second olefinic product by dimerising at least a portion of the intermediate fraction; and producing said third olefinic product that includes internal olefins by dehydrogenating a resultant paraffin fraction or at least a portion of the heavy fraction and optionally first separating alpha olefins from paraffins of the heavy fraction. separating said olefins-containing Fischer-Tropsch condensate into a light fraction which is a C 5 -C 7 fraction, an intermediate fraction which is a C 8 -C 15 fraction which includes paraffins and alpha-olefins and a heavy fraction which is a C 16 -C 22 fraction which includes paraffins and alpha-olefins; producing said first olefinic product that includes branched internal olefins by oligomerising at least a portion of the light fraction using a zeolitic catalyst under an oligomerisation pressure of less than 15 bar and with an average catalyst activity chosen to inhibit cyclo-paraffin and aromatic production and to promote production of branched internal olefins; carrying out either one or both of the steps (i) and (ii) of: (i) producing said second olefinic product (a) by dehydrogenating at least a portion of the intermediate fraction to convert paraffins to internal olefins and producing an intermediate product which includes internal olefins and alpha-olefins, and then (b) by synthesising higher olefins, by means of dimerisation or olefin metathesis, from the intermediate product which includes internal olefins and alpha-olefins and optionally first separating the alpha olefins from the paraffins of the intermediate fraction before (a); and (ii) producing said second olefinic product by dimerising at least a portion of the intermediate fraction; and producing said third olefinic product that includes internal olefins by dehydrogenating a resultant paraffin fraction or at least a portion of the heavy fraction and optionally first separating alpha olefins from paraffins of the heavy fraction. (i) producing said second olefinic product (a) by dehydrogenating at least a portion of the intermediate fraction to convert paraffins to internal olefins and producing an intermediate product which includes internal olefins and alpha-olefins, and then (b) by synthesising higher olefins, by means of dimerisation or olefin metathesis, from the intermediate product which includes internal olefins and alpha-olefins and optionally first separating the alpha olefins from the paraffins of the intermediate fraction before (a); and (ii) producing said second olefinic product by dimerising at least a portion of the intermediate fraction; and producing said third olefinic product that includes internal olefins by dehydrogenating a resultant paraffin fraction or at least a portion of the heavy fraction and optionally first separating alpha olefins from paraffins of the heavy fraction.