Process for evaluating the effect of a refinery feedstock on a refinery process by (i) providing a refinery feedstock (ii) treating the refinery feedstock to produce a plurality of fractions each representative of a feedstock for the refinery process, the plurality of fractions having at least two fractions with different properties; (iii) treating each of the plurality of fractions under experimental conditions representative of those in the refinery process, the treatments being carried out in an essentially parallel manner; and (iv) determining one or more performance criteria for each fraction for the refinery process by analyzing the respective product streams produced from each fraction at least partially in parallel.