Abstract: A hybrid fluid heating system for heating a production fluid using fuel and/or electric energy sources, the production fluid being contained in a pressure vessel includes a fuel-fired furnace heating subsystem, comprising: a furnace configured provide a thermal transfer fluid; and a heat exchanger configured to receive the thermal transfer fluid from the furnace and configured to be in thermal communication with the production fluid to provide convective heat exchange from the thermal transfer fluid to the production fluid; an electrical heating subsystem comprising one or more electrical heating elements disposed at least partially within the pressure vessel and being in contact with the production fluid; and wherein the fuel-fired furnace heating subsystem and the electrical heating subsystem are each configured to be individually controlled such that the production fluid is selectively heated by at least one of the fuel-fired furnace heating subsystem and the electrical heating subsystem.