The present invention relates to a hydrocracking reactor system and a process utilizing the same for upgrading heavy hydrocarbonaceous material to value-added products. Accordingly, an aspect of the present invention includes dispersing a liquid feedstock pre-mixed with a catalyst from top of a reactor vessel to obtain dispersed droplets having a predetermined droplet size less than 500 μm, introducing a gaseous feed comprising primarily of hydrogen from bottom of the reactor vessel to form a continuous gaseous phase throughout a cross-section of the reactor vessel, and allowing the dispersed droplets to contact the continuous gaseous phase throughout the cross-section of the reactor vessel to form reaction effluent comprising one or more lighter product hydrocarbons. The method may further include removing at least a top portion and at least a bottom portion of the reaction effluent from the reactor vessel.