In-situ combustion processes are largely a function of oil composition and rock mineralogy. The extent and nature of the chemical reactions between crude oil and injected air, as well as the heat generated, depend on the oil-matrix system. Laboratory studies, using crude and matrix from a prospective in-situ combustion project, should be performed before designing any field operation. The chemical reactions associated with in-situ combustion are complex and numerous. They occur over a broad temperature range.