The impact of decanoic acid (a model molecule representative of the most abundant oxygenates present in LTFT syncrude) and its by-products (CO, CO2, H2O) on the transformation of n-hexadecane was studied over a Pt/Al2O3-SiO2 conventional bifunctional catalyst under hydrocracking conditions. An irreversible impact of decanoic acid and its by-products (CO and CO2, H2O) was demonstrated corresponding to a decrease of the activity of the catalyst and a modification of the selectivities towards isomerization and cracking. Water produced by the total transformation of the acid, CO, CO2 was identified as the real contaminant whatever the oxygenates. The catalyst selectivities towards isomerization and cracking were modified in favour of isomerization in the presence of low amounts of oxygenates. The balance (acid and hydro-dehydrogenation properties) of the catalyst was modified corresponding to a decrease of the acidity of the support and a sintering of the platinum. (C) 2016 Elsevier B.V. All rights reserved.