The present work discusses the behavior of horizontal multiphase flows in the presence of a dense gas. This scenario has been important in the development of the Brazilian Pre-salt oil production but is timidly explored in the literature. Simulations considering real production scenarios show that the increase in CO2 content generates an uncertainty in the calculated results, mainly due to the introduction of a gas phase with density close to that of the liquid phase. An experimental apparatus is designed that permit operation in conditions in which the dense phase (represented in this study by the CO2) is in supercritical state. The experimental flow patterns and their comparison with maps in the literature in conditions where the gas is in the supercritical state, should allow an evaluation on the necessity (or not) for the specific modeling of this scenario. The proposed methodology includes the realization of an extensive test matrix which − according to the current knowledge - represents all observed flow patterns for water and air flows. Previous results show that the patterns predicted by the commercial simulators are not in agreement with the theoretical results of the maps obtained for water and air, when the fluids properties are extrapolated. In the proposed experimental apparatus, in order to reduce the uncertainties about multiphase flow in presence of high dense gas phase, the determination of the flow patterns is achieved through visualization in the presence of mineral oil and CO2 in a relative high pressure scenario.