The use of electromagnetic radiation, radiofrequency (RF) and microwaves (MW), for downhole dielectric heating has potential applications in enhanced/improved oil recovery processes (EOR). The Lambert’s equation was coupled to a commercial simulator in order to model reservoir dielectric heating. Using a MW heated (2.45 GHz) one-dimensional reactor, this mathematical model was validated in the presence of crude oil/sand cores. Three different conceptual reservoirs were evaluated which involved a medium crude oil (24°API), a shallow (1100 ft) Lake Maracaibo heavy oil (11°API) and a thin pay zone (20 ft) Orinoco Basin extraheavy crude (7.7°API). For all the cases evaluated, numerical simulation results showed an important acceleration in the oil production due to RF and MW heating which was attributed to reduction of crude viscosity coupled with favorable relative water-to-oil permeabilities. For example, in the shallow heavy oil case, RF heating led to an increase of 86% of the cumulative oil production in comparison with the cold production case, using 140 MHz at 50 kW over a ten-year period. Furthermore, calculated energy gains (measured as the ratio between the energy extracted as crude oil equivalent to energy added to the reservoir as electricity) were in the 8 to 20 range, indicating that the process is favorable from the thermodynamic point of view. These conceptual numerical simulation results indicate the high potential of dielectric heating technology for medium, heavy and extra-heavy EOR with possible field applications.