Many light and medium gravity oil reservoirs have and underlying contiguous water zone, in communication with the oil zone. As a result, a conventional waterflood is often unsuccessful because the injected water tends to channel into the more conductive bottom water layer. The research results discussed here show that modified waterfloods of such reservoirs may still be economically viable. Experiments were carries out in a three-dimensional model, employing a number of techniques, including horizontal wells. The flooding fluids consisted of polymer solutions and emulsions. The most successful strategy was to use a polymer solution as the mobility control fluid. Such a combination yielded oil recoveries approaching 70%, as compared to 50% for a conventional waterflood, for equally thick layers. The experimental results were correlated nu means of a three zone analytical model allowing for crossflow between oil and water layers, which is useful for predicting the performance of such floods. Experiments utilizing horizontal injector producer pairs for conventional waterfloods in the presence of water left as well as floods utilizing polymers and emulsions showed only limited gains over vertical well pairs. Guidelines are offered for the choice of well and fluid combinations for successful floods.