In this study, deposition of I2(g) on stainless steel tubing was investigated. The purpose was to quantify the rate of iodine deposition and desorption, as well as to elucidate the underlying mechanisms. The parameters included I2 gas phase concentration (10-7 to 10-11 M), relative humidity (<25 to 100%), tube surface temperature (23 to 90°C), and steel type (SS-304L and SS-316L). Gaseous I2 was found to deposit through both physical and chemical adsorption with deposition velocities ranging from 5 × 10-3 to 1.0 cm/s. At concentrations below 10-9 M, I2 rapidly deposited and was easily desorbed, consistent with physical adsorption. At concentrations above 10-9 M and low relative humidity (<25%), both adsorption and desorption were slow, consistent with a slow chemisorption process. At high relative humidity (>75%), rapid chemisorption with pitting corrosion occurred. Under some conditions, adsorption became inhibited resulting in an apparent maximum surface loading. At high iodine concentration, high relative humidity, and tube temperatures of 40 or 60°C, no such inhibition occurred, resulting in rapid and continuous iodine adsorption.