Deterioration of concrete structures in aggressive marine environments requires hundreds of millions of dollars in repair every year. To solve this problem, durability-based design methods must be created to find the most economical solution that provides the desired service life of the structure. A key step in these design methods is the accurate estimation of chloride diffusion into concrete. The DuraPGulf computer program described in this article employs field data in a semi-empirical durability design model to provide realistic predictions of corrosion initiation.