NOVELTY - At least a portion of hydrocarbon containing formation, is heated by heat source(s). The heat is transferred from the heat source to a selected section of the formation. The heat from the heat sources is controlled so that the average temperature in majority of selected section of formation, is less than 375 degreesC. Finally, a mixture is produced from the formation.    USE - For in situ conversion of hydrocarbons to produce hydrocarbons, hydrogen and/or novel product streams from underground hydrocarbon containing formations; for production of synthesis gas used as fuel, for synthesizing a wide range of organic and/or inorganic compounds such as hydrocarbons and ammonia, for generating electricity by reducing pressure of synthesis gas in turbines and/or using temperature of synthesis gas to form steam, used in energy generation units such as a molten carbonate fuel cell, a solid oxide fuel cell or other type of fuel cell, for production of branched and unbranched paraffins, for catalytic methylation to produce methane, for production of methanol, gasoline and diesel fuel, ammonia and middle distillates and for upgrading oils; and for production of carbon dioxide.    ADVANTAGE - The method yields relatively high quality hydrocarbon products, hydrogen and other products. Sequestering fluid formed within the formation significantly reduces or eliminates fluid that is released to the environment due to operation of the in situ conversion process. Superposition of heat may vary depending on spacing between heat sources. The spacing may be selected to increase the effectiveness of the heat sources, thereby increasing the economic viability of a selected in situ conversion process for hydrocarbons. Superposition of heat tends to increase the uniformity of distribution in the section of formation selected for treatment. An oxidizing fluid is used to inhibit carbon deposition. An energy input caused is reduced by heating a portion of formation by oxidation in combination with heating the portion of formation by electric heater. The oxidation reaction may be propagated slowly through a greater portion of formation so that fuel heat sources may be required to heat such a greater portion of formation. Controlling pressure, heat and/or heating rates of a selected section in the formation increases production of selected formation fluids.    DETAILED DESCRIPTION - At least a portion of hydrocarbon containing formation, is heated by heat source(s). The heat is transferred from the heat source to a selected section of the formation. The heat from the heat sources is controlled so that the average temperature in majority of selected section of formation, is less than 375 degreesC. Finally, a mixture is produced from the formation. The hydrocarbons are optionally partly hydrolyzed during heating. The thermal conductivity of the formation is at least 0.5 W/(m degreesC).    INDEPENDENT CLAIMS are included for the following:    (1) In situ method for heating hydrocarbon containing formation;    (2) In situ method for producing hydrogen from hydrocarbon containing formation;    (3) System configured to heat hydrocarbon containing formation;    (4) Method for forming heater wells in hydrocarbon containing formation;    (5) Mixture produced from a portion of hydrocarbon containing formation;    (6) In situ production of synthesis gas from hydrocarbon containing formation;    (7) Method of forming a spent portion of formation within hydrocarbon containing formation;    (8) Method of sequestering carbon dioxide within hydrocarbon containing formation;    (9) In situ production of energy from hydrocarbon containing formation; and    (10) Production of ammonia using carbon containing formation.