an approach for the evaluation of potential odor sources of refineries and storage tank farms is presented. The method comprises three steps: initial expert examination, estimation of odor emission rates, and dispersion calculations to predict odor perception frequencies in the neighborhood of the site under investigation. The aim is to quantify the effect of suspected odor emission sources, thus rating their relevancy in order to channel investment in the most effective way. Calculation methods and selected results of olfactory measurements are presented. The facts are illustrated by three actual case studies.