A method for in situ heating of a selected portion of a targeted organic-rich rock formation such as an oil shale formation is provided. The method includes the steps of providing casing in a wellbore extending to a depth within or below the selected portion of the organic-rich rock formation, and also providing a tubing within the casing. An annular region is formed between the tubing and the surrounding casing. Air or other oxidant and a combustible fuel are injected into the wellbore. Either the air or the combustible fuel is in stoichiometric combustion excess. The method also includes providing hardware in the wellbore so as to cause the air and the combustible fuel to mix and to combust at substantially the depth of the organic-rich rock formation. The hardware may include more than one burner. Insulation may be placed along the tubing adjacent the first burner in order to reduce the heat transfer coefficient within the tubing and to provide a more uniform temperature within the annulus.