Measurement of soil organic carbon (OC) is slow and expensive when inorganic carbon (IC) is present. Our objective was to develop an automated volumetric IC analysis system, thus allowing OC to be determined by difference. The system was developed by combining a pressure transducer with a personal computer (PC), data acquisition board, and appropriately developed software. The volumetric system was compared with combustion, neutralization, and sum of Ca + Mg techniques for samples containing up to 60 g kg−1 IC. Correlations between methods showed linear agreement (r2 ≥ 0.994). The volumetric system was more precise for relatively low IC amounts (2.0 g kg−1) and could process 20 samples h−1.