This method is for the determination of heptane-insolubles inpetroleum oils and is applicable to samples that are fluid at 80°Cor lower temperatures. This method covers the range of 0.01% toabout 20% heptane-insolubles. Solid particulate materialsinterfere. The method may also be used to determinetoluene-insolubles (see Note 1). More viscous or solid materialssuch as asphalts may be handled by the modification described inthe APPENDIX. The data provided by this method may beemployed as an index to the coking tendency of petroleum oils whenconsidering their suitability as charge stocks to cracking or otherprocesses.