Dry glycerol was etherified with com. isobutene fraction at 90 degrees C under pressure in a flow reactor (flow rate 18,7 to 95,9 mol/kg/h) filled with Amberlyst 35((R)) catalyst Mono-, tri- and mainly di-tert-butyl ethers of glycerol were found in the reaction product The glycerol conversion was 38,8 to 54,0%. The process was also studied directly on the product of the methanol transesterification of the rape - seed oil at 90 degrees C and 10 atm for 6 h. The highest degree of glycerol conversion was achieved when silica-supported Nation NR50 catalyst was used (up to 69,1%). The reaction product was tested as a component of the gas oil. Its addition resulted in an increase in cetane no. and decrease in viscosity and cold fifter plug point.