In order to assess quantitatively the sulfidation characteristics of industrially used alloys of copper, we have exposed a variety of copper‐nickel‐tin alloys as well as the pure metals to hydrogen sulfide in humidified air. The thicknesses of the resulting sulfide films were then determined. Nickel and tin were very resistant to sulfidation and copper alloys containing at least a combined total of 8% of these metals were resistant as well. The rate of sulfidation for the 92 Cu/4 Ni/4 Sn alloy is decreased with respect to copper by a factor of about four for moderate exposures. The rate continues to decrease as more alloying metal is added to the copper, reaching an equivalent rate of <0.2 nm for an alloy of 78 Cu/15 Ni/8 Sn in a typical field environment. The content of nickel in the alloy appears to be more important to the inhibition of sulfidation than the tin content. A spinodal alloy after heat‐treatment is less resistant to sulfidation than the same alloy as cold‐worked. Annealed 725 alloy (89 Cu/9 Ni/2 Sn) is more prone to initial sulfidation than is the same alloy when work hardened. The results of this and earlier work demonstrate that alloys of copper containing at least 10% of any of the common alloying metals are some thirty times more resistant to sulfidation than pure copper.