© 2022 Elsevier B.V.In situ combustion is one of the oldest enhanced oil recovery methods usually applied to heavy oil fields to improve recovery. In this process, air or oxygen-enriched gas is injected into a reservoir, burning some of the oil in place and generating heat and combustion gases. A considerable fraction of heavy oil resources resides in naturally fractured systems. There is no reported successful application of in situ combustion in a field with fractured systems in the literature to date. There is a limited number of studies regarding the subject in the literature. Thus, fundamental understanding of the process in fractured systems is limited. In this study, laboratory experiments of in situ combustion in core samples with the presence of fractures were conducted. A total of 12 combustion tube experiments were conducted with 12° API heavy oil from the Bati Raman field in Turkey. These experiments differ in their configuration of fractures and oxygen concentration in the injected gas. Based on our experimental observations three distinct behaviors were observed regarding front propagation through fractured systems. The first type is strictly diffusion-limited, the second type is characterized by a thick combustion front and the last is homogenous behavior. These observations could provide a fundamental basis for possible field applications of in situ combustion in fractured systems.