A system for in-situ heating of a subsurface formation for the extraction of hydrocarbons in underground deposits is disclosed. The system is configured to heat the underground deposit of hydrocarbons to facilitate fluid flow and hydrocarbon recovery from the underground deposit. The system has an antenna formed from a coaxial transmission line having an annular space between the transmission line outer conductor and the inner conductor and having one or more periodic aperture arrangements along the axial length of the outer conductor. A method for in-situ heating of a subsurface formation for recovering hydrocarbons contained therein is also disclosed. The method comprises: providing an antenna in the subsurface formation; providing electromagnetic RF power to the antenna for heating at least a portion of the subsurface formation.