"INTRODUCTION The American Petroleum Institute sponsored a symposium on evaporation loss * at the Thirty-second Annual Meeting in 1952. The symposium papers presented average figures for standing-storage loss from floating-roof tanks expressed as barrels per foot of diameter per year per pound of true vapor pressure. Wide variation in the data was noted and further effort on correlating test results was recommended. Losses from butt-welded tanks with close-fitting seals also required additional consideration. The API Evaporation Loss Committee@ in 1957@ collected from the petroleum industry both new and previously obtained data on evaporation loss from floating roof tanks. An intensive study was made of these data. As a result of this study@ the effect of an additional variable@ wind velocity@ was determined and the earlier variables were defined more precisely resulting in a significant reduction in the spread of data for the various types of floating-roof tanks. This bulletin presents the resultant correlations for use in estimating evaporation loss. To supplement the general description of equipment covered in API Bulletin 2513: Evaporation Loss in the Petroleum industry-Causes and Control@ information is presented herein which deals with the vital seal portion of the floating roof. In addition to the metallic-shoe type of seal@ the nonmetallic seal is discussed and a comparison is made of the features of each. A guide to the selection@ maintenance@ and replacement of the floating-roof seal-based on manufacturers' publications@ users' experience@ and tests-is included in this bulletin. * ""Symposium on Evaporation Loss@"" Proc. API 32 [I] 213-81 (1952)."