This method is for the determination of either heptane or toluene insoluble material in petroleum oils. This method covers the range of 0.01 to 25 mass-% insolubles. Solid particulate materials interfere. More viscous or solid materials such as asphalts may be analyzed using this method but will require using a heated sonicating bath (up to 60°,C). The data provided by this method may be used as an index to coking tendency of petroleum oils when considering their suitability as charge stocks to cracking or other processes.