Wettability has a strong impact on many oil recovery processes. However, the determination and restoration of reservoir wettability in the laboratory is still problematic, due to the difficulty in reproducing reservoir conditions. Wettability changes are usually achieved in the laboratory by aging the rock samples with selected crude oils, or by chemical treatment of the solid surfaces. The objective of this work is to study the effects of wettability alteration, by aging silica gels, placed within a porous medium, on the ability of oil and water to flow through that medium. A series of experiments was performed to visualise oil and water flow through a porous medium containing silica gel. The experiments were conducted in transparent glass models in which the flow events and the fluid distribution were clearly visible and could be recorded. To form the gel in situ, an alkyl silicate gelant was used, which is soluble in an organic phase, and which, when in contact with water, reacts to convert the water phase into a gel. The newly formed silica gel is water-wet, but when aged in paraffin, interesting changes are observed over time: the surface wettability changes to finally become oil-wet, while small cracks develop within the gel structure. The gel was placed in both strongly water-wet and oil-wet models, which, combined with the gel behaviour, generated a wide range of flow and wettability conditions, i.e., water-wet, intermediate-wet, mixed-wet and oil-wet. The visual observations are complemented by measurements of end-point relative permeabilities, allowing the demonstration of the effects of wettability upon relative permeability. The fluid distribution at pore level and the hierarchy of wetting determine the flow characteristics. The high values of both oil and water relative permeabilities correspond to the strongly wetting conditions, which agrees with the traditional description of oil–water distribution within porous media. On the other hand, the intermediate-wet case has the lower oil and water relative permeability, with the oil permeability proportional to the fraction of the surface that is oil-wet. The mixed-wet cases have intermediate oil and water permeability, but show an increase in water relative permeability as the amount of water-wet surface decreases. These results have important implications in the design and performance of wellbore gel treatments, which are used to modify water and oil flow behaviour.