A gasometric technique for determining the amount of CaCO 3 in sediments has been adapted to the commercially-available LECO (Laboratory Equipment Corporation) machine used to determine the total carbon content. The volumetric absorption of CO 2 by KOH in the method described is both accurate and precise. Organic carbon values can also be obtained by difference and are more reliable than values obtained by separate techniques. One technician can analyze at least 75 samples in an 8-hour day. Use of sediment pellets rather than powdered material contributes to greater accuracy, because error in sample weight caused by an increase in the moisture content is reduced.