By treatment with CrCl2, the radical populations of Kimmeridge and Bakken kerogens were significantly decreased. When both kerogens are mildly heated, anhydride formation at low temperatures can be detected by infrared spectroscopy only when radicals have been removed by CrCl2 treatment. The "native" kerogen radicals react with thermally formed carboxylic acid anhydrides to form esters and CO. Some of the observable kerogen radicals are persistent and reactive. The Acholla and Orr method for pyrite removal also reduces the radical population of these kerogens.