A process for treating a hydrocarbon-containing feedstock is provided in which a hydrocarbon-containing feed comprising at least 20 wt. % of heavy hydrocarbons is mixed with hydrogen and at least one catalyst to produce a hydrocarbon-containing product. The hydrocarbon-containing feedstock, the catalyst(s), and the hydrogen are provided to a mixing zone and blended in the mixing zone at a temperature of from 375° C. to 500° C. A vapor comprised of hydrocarbons that are vaporizable at the temperature and pressure within the mixing zone is separated from the mixing zone, and, apart from the mixing zone, the vapor is condensed to produce a liquid hydrocarbon-containing product. The hydrocarbon-containing feedstock is continuously or intermittently provided to the mixing zone at a rate of at least 350 kg/hr per m3 of the mixture volume in the mixing zone.