A method which uses a controlled loss on ignition for the determination of CO 2 in carbonate rocks was developed to provide a simple and reliable means of producing results from a group of samples at the same time. The routine loss on ignition was modified slightly to include 2 steps instead of one. A loss of 550 degrees C. is recorded as well as the loss at 1,000 degrees C. Thus, by accurately controlling the temperature, values were obtained for the carbonate and noncarbonate portions of the loss on ignition. The method is demonstrated to be rapid and as reliable as acid evolution methods. Differential thermal analysis technique was used to aid in time and temperature selections. DTA curves, experimental data, and procedures are shown.