TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: The method further comprises controlling a pressure and the temperature within the selected section/volume of the formation; controlling formation conditions so that the produced mixture comprises a partial pressure of hydrogen with the mixture greater than 0.5 bar; altering the pressure within the formation to inhibit production of hydrocarbons from the formation having carbon numbers greater than 25; providing hydrogen to the heated section to hydrogenate hydrocarbons within the section; heating a portion of the section with heat from hydrogenation; controlling the heat to yield condensable hydrocarbons; separating the produced mixture into a gas stream (813) and a liquid stream (811); and separating the liquid stream into an aqueous stream and a non-aqueous stream. The formation conditions are controlled by recirculating a portion of hydrogen from the mixture into the formation.Preferred Process: The mixture is produced in the production well, where three quarters (in triangular formation) or at least7 heat sources are disposed in the formation for each production well. The mixture can be produced from the formation as a vapor.Preferred Function: The production well is heated to prevent condensation of the mixture within the wellbore. The pressure is controlled to control the amount of condensable hydrocarbons; and to control the API gravity of condensable hydrocarbons within the produced mixture. The heat is controlled so that coke production is inhibited. The heat pyrolyzes the hydrocarbon(s) within the selected section of the formation. It is controlled to give a yield greater than 60 wt.% of condensable hydrocarbons as measured by Fischer Assay.Preferred Condition: The heat is generated from electrical heaters (803), surface burners, flameless distributed combustors, or natural distributed combustors. It is transferred to the selected portion by conduction or by increasing a permeability of the selected section to greater than 100 millidarcy. When the pressure is reduced the production of condensable hydrocarbons is increased. When the pressure is increased the production of non-condensable hydrocarbons is increased. The pressure is controlled as a function of temperature or vice versa. The heating energy/day provided to the volume of the hydrocarbon containing formation is equal to or less than the heating energy/day (Pwr) which is calculated using the mathematical expression: Pwr = hasteriskVasteriskCvrho-B; where h is an average heating rate (less than 10degreesC/day) of the formation; V is the selected volume of the hydrocarbon; Cv is the average heat capacity; and rho-B is formation bulk density. The pressure is controlled using the mathematical expression: pbar greater than e-((-A/T)+B-2.6477); where p is the pressure in bar absolute; T is the temperature in degrees Kelvin; and A and B are parameters that are larger than 10 and are selected in relation to the characteristics and composition of the hydrocarbon containing formation and on the required olefin content and carbon number of the pyrolyzed hydrocarbon fluids.Preferred Parameters: The average temperature within the selected section is less than 375degreesC to inhibit the production of hydrocarbons having carbon numbers greater than 25. The controlled pressure is atmospheric to below 100 bar absolute, preferably at least 2.0 bar absolute. The heat is controlled so that an average heating rate of the selected section/volume is less than 1degreesC/day during pyrolysis. The minimum pyrolysis temperature is 270degreesC. The thermal conductivity of portion(s) of the selected section is greater than 0.5 W/(mdegreesC). The heating rate is less than 10degreesC/day.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Product: The produced mixture comprises condensable hydrocarbons (60 wt.% as measured by the Fisher Assay) having an API gravity of at least 25degrees; non-condensable hydrocarbons comprising ethene and ethane having a molar ratio of 0.001-0.15; ammonia (0.05 wt.%); hydrogen sulfide; and carbon dioxide. Preferred Composition: The (non)condensable hydrocarbons are olefins (0.1-15 wt.%).Preferred Condition: The average carbon number of the produced mixture is 1-25.Preferred Component: The condensable hydrocarbon comprises (wt.% calculated on an atomic basis) nitrogen (1); oxygen (1); oxygen containing compounds comprising phenols (5-30); sulfur (less than 1); aromatic compounds (greater than 20%); multi-ring aromatics with more than two rings (less than 5); asphaltenes (less than 0.3); and cycloalkanes (5-30 wt.%). The non-condensable component comprises hydrogen (greater than 10 to less than 80 vol.% of the non-condensable component). EXAMPLE - Laboratory experiments were conducted on tar samples contained in their natural sand matrix. The core material received from a well was mixed and split. One aliquot of the slit core material was used in the retort and the replicate aliquot was saved for comparative analysis. The heating rate was 10degreesC/day and was operated at no backpressure 1 bar absolute. The internal temperature of the run was raised from ambient to 110degreesC, 200degreesC, 225degreesC and 270degreesC with 24 hours holding time between each temperature increase. Most of the moisture was removed from the samples during heating. Beginning at 270degreesC, the temperature was increased by 1degreesC/day, 5degreesC/day or 10degreesC/day until no further fluid was produced. The temperature was monitored and controlled during the heating of this stage. Produced liquid and gas were collected. The gas comprises (wt.%) hydrogen (11.28); nitrogen (1.87); oxygen (5.96) and sulfur (4.32).