A hydrocarbon containing formation may be treated using an in situ thermal
process. A mixture of hydrocarbons, H.sub.2, and/or other formation fluids
may be produced from the formation. Heat may be applied to the formation
to raise a temperature of a portion of the formation to a pyrolysis
temperature. Pressure within the formation may be controlled as a function
of temperature or temperature within the formation may be controlled as a
function of pressure to yield a desired mixture.
