A continuous flow method (CF-IRMS) for the rapid determination of the sulfur isotope composition of sulfide and sulfate minerals has significant advantages over the classic extraction method in terms of the reduced sample quantity and a rapid analytical cycle of less than 8 min/analysis. For optimum performance, the technique is sensitive to a number of operating parameters, including sample weight and the O₂ saturation of the Cu-reduction reactor. Raw data are corrected using a calibration based on five international and internal standards ranging from −17.3 to +20.3‰, which requires monitoring in order to correct the effect of changing δ¹⁸O of the sample gas on the measured mass 66 values. Measured sulfur contents are within 1−1.5% of expected values and the reproducibility of δ³⁴S values is ±0.1‰ (1σ). The technique has been used successfully for more than 1000 analyses of geological samples with a wide range of δ³⁴S from −20 to +20‰.