Overall, oil-laden fractured-rock reservoirs contain between 25 and 30 percent of the total known global petroleum reserves. In these reservoirs, fractures are the dominant flow path, therefore economic oil recoveries from fractured reservoirs rely on better understanding of the flow in fractures and networks of fractures. However, in contrast with gas-liquid flow in fractures, the flow of heavy oil and water has received less attention. Particularly, the flow regime map for two-phase immiscible flow in a thin gap and the transition boundaries are not well studied yet. In this research, a Hele-Shaw apparatus was used to study the flow of water in the presence of heavy oil in a smooth walled fracture. Different flow patterns were observed under different flow conditions and the effects of different fluid and fracture properties on flow regime transition boundaries for a thin gap were evaluated. The results of the experiments demonstrate that, flow regime boundaries strongly depend on fluid and fracture properties. The results also reveal that one correlation can be applied to predict different transition conditions under different fracture orientation.