A process for reducing the viscosity of a liquid hydrocarbon feedstock into lower molecular weight hydrocarbon compounds in a hydrovisbreaking reaction zone comprising: a. mixing a catalyst to the feedstock in the form of finely dispersed solid material or soluble catalyst in the hydrocarbon feedstock; b. mixing the liquid hydrocarbon feedstock, the catalyst and an excess of hydrogen gas, in a mixing zone to dissolve a portion of the hydrogen gas in the liquid hydrocarbon feedstock and produce a two-phase mixture of a hydrogen-enriched liquid hydrocarbon feedstock and the remaining excess hydrogen gas; c. introducing the mixture of hydrogen gas, catalyst, and the hydrogen-enriched liquid hydrocarbon feedstock into a flashing zone under predetermined conditions to separate the undissolved excess hydrogen gas and optimize the amount of hydrogen dissolved in the hydrogen-enhanced liquid hydrocarbon feedstock, and recovering a single-phase hydrogen-enriched liquid hydrocarbon feedstock, wherein the flashing zone is maintained at a pressure in the range of 10 to 200 bars and a temperature in the range of 350 to 600°C; d. conveying the single-phase hydrogen-enriched liquid hydrocarbon feedstock under conditions that maximize the amount of dissolved hydrogen in the hydrocarbon feedstock into a hydrovisbreaking reaction zone in the presence of steam to crack the feedstock into relatively smaller molecules, wherein the hydrovisbreaking reaction zone operates: as a coil hydrovisbreaking reactor under a pressure in the range of 10 to 200 bars, a temperature in the range of 350 to 600°C, and with a residence time of from 0.1 to 60 minutes, or as a soaker hydrovisbreaking reactor under a pressure in the range of 10 to 200 bars, a temperature in the range of 350 to 600°C, and with a residence time of from 1 to 120 minutes; and e. recovering converted hydrocarbon products of reduced viscosity from the hydrovisbreaking reaction zone. a. mixing a catalyst to the feedstock in the form of finely dispersed solid material or soluble catalyst in the hydrocarbon feedstock; b. mixing the liquid hydrocarbon feedstock, the catalyst and an excess of hydrogen gas, in a mixing zone to dissolve a portion of the hydrogen gas in the liquid hydrocarbon feedstock and produce a two-phase mixture of a hydrogen-enriched liquid hydrocarbon feedstock and the remaining excess hydrogen gas; c. introducing the mixture of hydrogen gas, catalyst, and the hydrogen-enriched liquid hydrocarbon feedstock into a flashing zone under predetermined conditions to separate the undissolved excess hydrogen gas and optimize the amount of hydrogen dissolved in the hydrogen-enhanced liquid hydrocarbon feedstock, and recovering a single-phase hydrogen-enriched liquid hydrocarbon feedstock, wherein the flashing zone is maintained at a pressure in the range of 10 to 200 bars and a temperature in the range of 350 to 600°C; d. conveying the single-phase hydrogen-enriched liquid hydrocarbon feedstock under conditions that maximize the amount of dissolved hydrogen in the hydrocarbon feedstock into a hydrovisbreaking reaction zone in the presence of steam to crack the feedstock into relatively smaller molecules, wherein the hydrovisbreaking reaction zone operates: as a coil hydrovisbreaking reactor under a pressure in the range of 10 to 200 bars, a temperature in the range of 350 to 600°C, and with a residence time of from 0.1 to 60 minutes, or as a soaker hydrovisbreaking reactor under a pressure in the range of 10 to 200 bars, a temperature in the range of 350 to 600°C, and with a residence time of from 1 to 120 minutes; and e. recovering converted hydrocarbon products of reduced viscosity from the hydrovisbreaking reaction zone.