TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The superposition of heat from at least two heat sources pyrolyzes at least some hydrocarbons within selected section of formation. The formation conditions are controlled by maintaining a temperature within pyrolysis temperature range. Heat is supplied to a portion of the formation by heating a selected volume (V) of the formation which has a average heat capacity (Cv) and heating energy/day provided to the volume is equal to or less than Pwr which is calculated using the equation: Pwr=hxVxCvxrhoV, where Pwr is the heating energy/day, h is the average heating range of formation, rhoV is the formation bulk density. The heating rate is less than about 10degreesC/day. Pressure is controlled within at least the majority of selected section of formation with a valve coupled to a production well located in the formation. Preferably, the pressure is controlled to at least about 2.0 bar absolute. The conditions are controlled such that the produced mixture comprises a partial pressure hydrogen within the mixture greater than about 0.5 bar. The formation conditions are controlled by recirculating a portion of hydrogen of the mixture into the formation. Pressure is altered within the formation to inhibit production of hydrocarbons from the formation having carbon number greater than about 25. Hydrogen is supplied to heat section to hydrogenate hydrocarbons within the section and portion of the section is heated with heat generated by hydrogenation. The heat transfer involves increasing permeability of majority of selected section to greater than about 100 millidarcy. The pressure is reduced to increase production of condensable hydrocarbons and pressure is increased to increase the production of non-condensable hydrocarbons. Pressure within the formation is controlled from atmospheric pressure to about 100 bar, as measured at a wellhead of production well, to control API gravity of condensable hydrocarbon within the produced mixture, where the pressure is reduced to decrease the API gravity and pressure is increased to reduce the API gravity. Preferred Mixture: The produced mixture comprises condensable hydrocarbons or non-condensable hydrocarbons. About 0.1-16 weight% (wt.%) of condensable and non-condensable hydrocarbons are olefins. The condensable hydrocarbon contains less than about 1 wt.% of each of nitrogen, sulfur and oxygen. About 30 wt.% of condensable hydrocarbon comprise oxygen containing carbon (phenol). Greater 20 wt.% of condensable hydrocarbons are aromatic compounds, less than 5 wt.% are multi-ring aromatics, less than 0.3 wt.% are asphalt and 5-30 wt.% are cycloalkanes.