This paper compiles aspects on the corrosivity of hydrocarbon fluids in oil pipelines. Oil pipelines carry complex mixtures of hydrocarbons, water, gases, and miscellaneous chemicals that, in relation to the physico-chemical and flow conditions, drive internal corrosion in a variety of ways. The paper highlights the water-oil emulsions and multiphase flow regimes, wettability of metal surface, corrosivity of aqueous phase in crude oil, composition of the aqueous phases in hydrocarbon fluids, roles of O₂, CO₂, sulfur and H₂S in the hydrocarbon fluids, and influence of oil chemistry on the corrosivity of the aqueous phase.