Infrared spectra confirm that, when heated to 200 degrees C, Bakken kerogens form anhydrides from carboxylic acids. The anhydrides in turn thermally decompose at temperatures below 250 degrees C. The thermal production of CO, the absence of CO2, and the low temperature of the anhydride decomposition are all consistent with a radical chain mechanism initiated by a kerogen radical. Anhydride decomposition occurs by addition of a radical to the anhydride carbonyl to form an ester and to liberate an acyl radical that rapidly loses CO to form an alkyl radical to continue the chain. This pathway is one of several by which kerogens thermally decarboxylate.