Production of heavy and extra-heavy crude oils generally entails high costs, especially in the winter season, due to heat losses. This work studies the effect of a flow enhancer (a chemical formulation based on biodiesel and oxidized biodiesel of soy oil) on the viscosity of heavy crude oil from different wells in Northern Mexico. The observed results indicate a non-linear decreasing behavior of viscosity concerning temperature and volume fraction of the viscosity reducer. It is also presented a theoretical model that predicts the flow increase that can be achieved using the enhancer in systems in which crude oil temperature is higher than the temperature of the environment. Results showed adequate correspondence between experimental and predicted data. It was found that the enhancer increases the volume of crude oil that can be processed without varying pressure gradient.