A crude assay is a detailed chemical analysis of a crude oil that describes the volumes and qualities of different refined products that will result from processing the crude through a refinery.

The assay includes an estimate of the volumes of different distillation cuts or fractions that will result from processing a crude through a crude distillation unit. This is described in terms of the volume of crude that evaporates at different temperature ranges (or boiling points). Typically, an assay contains nine distillation cuts ranging from refinery gas to vacuum residuum.

For each distillation cut, the assay will also provide a number of quality characteristics. These include properties that affect how the cut will perform when processed through a conversion unit (e.g., density, concarbon, N+2A) and properties that affect the quality of any resulting product that the cut is blended into (e.g., cetane, octane, sulfur).

Links to assays for some of the more commonly use crudes are provided here: assay data