Contaminant carbon (blank carbon) was studied for its impact on the carbon isotope measurements (Δ14C and δ13C) of 3 organic compound classes of oceanic particulate organic matter. Two methods of blank correction and associated uncertainties were studied. First, the carbon blanks were quantified manometrically and the isotope ratios of the blank carbon were measured directly. Second, the isotope ratios of the blank carbon were estimated using the standard dilution method from the difference in Δ14C values between unprocessed and processed standards. The 2 methods agreed within the uncertainties. The standard deviations of numerous Δ14C measurements made on processed standard compounds were comparable to those of real samples. Blank correction using the standard dilution method is much less sensitive to the error in determination of blank carbon mass than is correction using the directly measured mass and Δ14C values of the blank carbon. The standard dilution method is recommended for correcting Δ14C analyses of small samples that involve incorporation of a significant amount of blank carbon.