Classical industrial hydrate risk evaluation schemes are commonly based on water dew-point calculation. This method ignores another (new) route to hydrate formation based on adsorption of water onto rusty surfaces. Maximum allowable water contents in pure and mixtures of hydrate formers of Structures I and II hydrocarbons to avoid the risk of hydrate nucleation during pipeline transport have been studied using both the dew-point method and the new approach of adsorption of water onto hematite (rust). The estimates from this study suggest that the new approach (adsorption of water onto the rusty internal walls of pipelines and equipment) dominates. Thus, this approach could have an impact on designing natural gas dehydration systems. Free energy analysis has also been performed to show which molecule forms hydrate first based on the combined first and second laws of thermodynamics in terms of Gibbs free energy. (c) 2018 American Institute of Chemical Engineers