The instant invention relates to an upflow for upgrading heavy oil feed stock and a method for upgrading heavy oil feed stock employing an upflow reactor and with a slurry catalyst. In one embodiment, the upflow reactor is a liquid recirculating reactor, which is operated in manner corresponding to a dispersed bubble flow regime, which requires a high liquid to gas ratio. A dispersed bubble flow regime results in more even flow patterns, increasing the amount of liquid, i.e., heavy oil feed stock that can be upgraded in a single reactor.