A world-wide test program was undertaken by ASTM Task Group Gl.09.02.03 to assess the relative corrosivity of seawater at 14 test sites. Aluminum alloy 5086 (UNS A95086), 90/10 copper-nickel (UNS C70600), and copper-bearing carbon steel (UNS K01501) test specimens were prepared at one location, shipped to the various sites, and returned to the original location for final evaluations. Results obtained through five years of testing indicate that corrosion behavior was generally within the limits of previously published results. The results show that while seawater is a ubiquitous environment, and quite similar in terms of chloride content and pH, the corrosivity is site- specific, and likely to be influenced by a myriad of other factors such as temperature, dissolved oxygen concentration, flow, degree of fouling, bacterial activity, pollution, etc. All of these factors are themselves often interrelated. The cooperation of all program participants has contributed much toward accomplishment of the objectives. More frequent monitoring of seawater variables at an exposure site is always helpful in better interpretation of the results of corrosion tests performed there. All of the 0.5 through 5-year exposure data are presented here; any typographical errors in the 0.5 through 3-year exposure data published previously have been corrected.