Bakken kerogens react rapidly when heated at temperatures of 40−180 °C to form carboxylic acid anhydrides and water from carboxylic acids. Differential scanning calorimetry (DSC) shows a pronounced irreversible endotherm over this temperature range, demonstrating the occurrence of an endothermic chemical reaction. The fact that this reaction is the formation of an acid anhydride was demonstrated using Fourier transform infrared (FTIR) spectroscopy. The amount of anhydride formed can be estimated by measuring the enthalpy of the process using DSC. Approximately 20% of the anhydride is hydrolyzed when the reacted kerogen has been allowed to stand in air at room temperature for three weeks, demonstrating that water has access predominantly to the kerogen surface during this time. Exposure of the kerogen to water vapor at 150 °C for 48 h results in complete anhydride hydrolysis. Swelling the kerogen with 95 vol% tetrahydrofuran (THF)−5 vol% water also results in only partial hydrolysis of the anhydride; howev...