Suppressing effects on oil genesis during coal and kerogen pyrolysis can be correlated with oxygen content. In the present work oil suppression has been tentatively corrected by modeling. A plot of the corrected oil yield vs rank was found to resemble a Van Krevelen’s H/C vs O/C diagram, and mass balance was consistent with a loss of oil potential in the early stage of coalification. Selective modifications of the oxygen groups of a lignite and of a bituminous vitrain were performed to test the above computations. The decarboxylation and dehydroxylation before pyrolysis resulted in a substantial increase and acceleration of oil formation.