The influence of presulfidation and H2S cofeeding on the carbon formation on SS304 alloy in the ethane-steam cracker was investigated in a laboratory-scale quartz reactor setup. SS304H coupons and SS304L powder samples were exposed to ethane-steam and dry ethane in varying H2S content (0-50 ppm), and the SS304 samples were characterized by scanning electron microscopy. This study shows that H2S cofeeding decreases catalytic carbon formation; while it increases the pyrolytic carbon formation during ethane-steam cracking. Preoxidation, presulfidation, and addition of steam to ethane feed also reduces the amount of catalytic carbon formed on the SS304H surface in short-term experiments (4 h). Presulfidation and addition of H2S to ethane feed significantly influences the shape and size of the carbon formed on the surfaces of investigated metal alloys. Presulfidation and H2S cofeeding reduced spalling of the SS304H coupon surface during coking/decoking and thermal cycling.