NOVELTY - In situ treatment of a hydrocarbon containing formation comprises: (1) providing heat from at least one heat source (801) to at least one portion of the formation: (2) allowing the heat to transfer from the heat source(s) to a selected section of the formation; (3) controlling the heat so that an average temperature in majority of selected section of the formation is less than 375degreesC and (4) producing a mixture.    USE - Used for in situ conversion of hydrocarbons to produce hydrocarbons, hydrogen and/or product streams from underground hydrocarbon containing formations, and for production of synthesis gas from hydrocarbon containing formation. The synthesis gas is used as fuel, for synthesizing a wide range of organic and/or inorganic compounds such as hydrocarbons and ammonia, branched and unbranched paraffins, methanol, gasoline and diesel fuel, ammonia and middle distillates and carbon dioxide, for upgrading oils, for generating electricity by reducing pressure of synthesis gas in turbines and/or using temperature of synthesis gas to form steam, and in energy generation units such as a molten carbonate fuel cell, a solid oxide fuel cell or other type of fuel cell.    ADVANTAGE - High quality hydrocarbon products, hydrogen and other products are produced by in situ treatment of the hydrocarbon containing formation. Sequestering fluid formed within the formation significantly reduces or eliminates fluid that is released to the environment due to operation of 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, 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. Controlling pressure, heat and/or heating rates of a selected section in the formation increases production of selected formation fluids.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) in situ heating of a hydrocarbon containing formation;    (2) in situ production of hydrogen from a hydrocarbon containing formation;    (3) formation of heater wells in a hydrocarbon containing formation;    (4) a system configured to heat a hydrocarbon containing formation;    (5) a mixture produced from a portion of hydrocarbon containing formation;    (6) in situ production of synthesis gas from a hydrocarbon containing formation;    (7) formation of a spent portion of a formation within hydrocarbon containing formation;    (8) sequestering carbon dioxide within a hydrocarbon containing formation;    (9) in situ production of energy from hydrocarbon containing formation; and    (10) production of ammonia using a carbon containing formation.    DESCRIPTION OF DRAWING(S) - The drawing shows the generation of synthesis gas in the hydrocarbon containing formation using pyrolysis water.    Heat source (801)    Electric heater (803)    Pyrolysis fluid (807)    Separator (809)    Aqueous stream (811)    Vapor stream (813)    Hydrocarbon condensate stream (815)    Synthesis gas generating fluid (821)    Synthesis gas (823)    Synthesis gas production well (825)