Abstract: A method and apparatus for controlling fluency of hydrocarbon fluids having a kinematic viscosity in the range of 350 seconds Saybolt Universal to 10,000 seconds Saybolt Universal at 100.degree. F. Electromagnetic waves generated by a power source are directed through a dielectric medium towards a contained hydrocarbon fluid of the foregoing type. The electromagnetic energy is converted into thermal energy within the hydrocarbon fluid for controlling its fluency.