Although incompatible crude oils have not been previously discussed in the scientific literature, they are discovered to be relatively common. Consequently, with the need of a predictive method, the Oil Compatibility Model was derived from two hypotheses. One hypothesis is that asphaltenes precipitate from the oil at the same mixture solubility parameter, no matter that the oil is blended with noncomplexing liquids or another oil. The other hypothesis is that the solubility parameter of a mixture is the volumetric average solubility parameter. As a result, the solubility parameter of a crude oil and its flocculation solubility parameter on a toluene-n-heptane scale can be determined based upon mixing the crude oil with toluene and n-heptane and determining if each mixture dissolves or precipitates asphaltenes. Thereafter, the correct proportions and correct order of blending oils to ensure compatibility can be specified. A refinery example is given where determining the correct order of blending potentially incompatible crude oils mitigated the coking of vacuum pipestill furnace tubes.