Gas oil for undergoing sulphuric acid processing involving the addition to the basic products of 98 % sulphuric acid in a quantity of 10 litres per 100 m3 ... followed by neutralization with 20 % sodium hydroxide solution in a quantity of 38 litres per 100 m3 ... and subsequent treatment with activated carbon by forced percolation under pump pressure in a filter of about 5 m3.