The distribution of hydrogen compounds between 50 km and the exobase is calculated subject to the condition that the upward flux of hydrogen atoms be sufficient to supply the thermal escape flux. The effect of varying many parameters, such as exospheric temperature, chemical rate constants, solar UV flux, and atmospheric transport coefficients is explored. It is found that H2 plays an important role in the chemistry and transport even above 100 km. It is found that the escape flux is determined mainly by the total mixing ratio and relatively insensitive to other factors at exospheric temperatures above 1000K, but is limited by the exosbase flow at lower temperatures. A thermal escape flux of 7×107 cm2 sec1 above 1000K is difficult to reconcile with a combine mixing ratio of H2O, H2 and CH4 greater than about 2 ppm at 50 km.