This paper presents an alternative methodology, based on a cost optimization model, for evaluating some effects of the implementation of an alternative Demand Response (RD) program based on Day Ahead Real-Time Pricing (DA-RTP) in electricity markets.The proposed methodology has three special characteristics: the first one is to assume that users can modify their consumption patterns without altering the quantity demanded daily; second one, user's flexibility to shift demand between hours depend of the kind of user and the time (peak vs off peak hours); finally, consumers have limited capability to shift demand outside of certain periods within the day.The model is tested with a simulation exercise for the Colombian electricity market.The results show a significant improvement in system and market performance, including consumer savings, a flattened load curve, and reduced operational risk in the system.