Petroleum upgrading process

A system for upgrading a petroleum feedstock, the system comprising:

• a petroleum feedstock;
• a water feed;
• means for heating and pressurizing said petroleum feedstock and water feed, wherein said means for heating and pressurizing the water feed are operable to produce a supercritical water;
• a first hydrothermal reactor, said first hydrothermal reactor in fluid communication with the petroleum feedstock and water feed, and being operable to maintain a reactor temperature and pressure sufficient to maintain water in its supercritical state;
• a second hydrothermal reactor, said second hydrothermal reactor in fluid communication with an outlet of the first hydrothermal reactor, wherein the second hydrothermal reactor is maintained at a temperature between 100° C. and 300° C., wherein water present in the second hydrothermal reactor is maintained in a liquid phase;
• and
• a separator in fluid communication with an outlet of the second hydrothermal reactor, said separator configured to separate water and hydrocarbon containing liquids.