The environmental constraints coming into place on aromatics in petroleum products makes it necessary to develop an analytical technique that explicitly accounts for their effect. Furthermore, the multicomponent nature of petroleum fractions makes it difficult to analyze feed composition sensitivities without a large number of tests. This paper presents a convenient way to analyze the sensitivity or, as sometimes called, the switchabilily of petroleum fractionators. The technique depends on “lumping” all the paraffinics, naphthenic and aromatic components into three “pseudo components”:P, NandA.