A process for oligomerizing a Fischer-Tropsch derived feed containing oxygenates which comprises (a) reducing significantly the oxygenates present in the Fischer-Tropsch derived feed by contacting said feed with a hydrotreating catalyst under hydrotreating conditions in a hydrotreating zone (8) and recovering from the hydrotreating zone a Fischer-Tropsch derived hydrotreated feed (10) which contains a significantly reduced amount of oxygenates as compared to the Fischer-Tropsch derived feed and also a significant amount of paraffins; (b) pyrolyzing the Fischer-Tropsch derived hydrotreated feed in a thermal cracking zone (12) under thermal cracking conditions pre-selected to crack the paraffin molecules to form olefins and collecting an olefin-enriched Fischer-Tropsch feed (14) from the thermal cracking zone (14); (c) contacting the olefin-enriched Fischer-Tropsch feed with a Lewis acid ionic liquid catalyst in an oligomerization zone (16) under oligomerization reaction conditions; and (d) recovering from the oligomerization zone a Fischer-Tropsch derived product (18) having molecules characterized by a higher average molecular weight and increased branching as compared to the Fischer-Tropsch derived feed.