In a process for the catalytic conversion of organic oxygenates to hydrocarbons, a feed comprising at least one organic oxygenate is contacted with a zeolite catalyst under conditions effective to produce a hydrocarbon product comprising aromatics, olefins and paraffins. At least a fraction of the hydrocarbon product containing C4+ hydrocarbons, including at least part of the olefins, is then contacted with hydrogen in the presence of a hydrogenation catalyst under conditions effective to saturate at least part of the olefins in the C4+-containing fraction and produce a hydrogenated effluent containing less than 1 wt % olefins. The hydrogenated effluent is useful as a diluent for heavy crude oils.