There are nearly 920,000 oil-producing wells worldwide, approximately 87% of which are operated with an artificial-lift method. A rough distribution of these wells shows that 71% use a beam-pumping system, 16% use electrical submersible pumps, 7% use gas lift, and 6% use other forms of lifting systems (Alemi et al. 2011; Liu and Qi. 2011; Ghareeb et al. 2007; Xu et al. 2012). The great majority of the world’s oil wells are on artificial lift; therefore, they require large amounts of external electric energy to produce hydrocarbons because the available formation energy is not sufficient to move the well fluids to the surface. On the basis of the 920,000 wells, with 10 kW/hr of consumed power for each well and oil production for 350 days of the year, beam-pumping systems consume approximately 4.77×1010 kW-hr of power per year worldwide. If the power consumption can be decreased by 20% with an energy-saving technique, that alone will help to save 0.95×1010 kW-hr of electricity per year around the world. Therefore, enormous economic benefits will be created by enhancing the system efficiency and reducing the consumption of energy. In this paper, a new comprehensive simulation method of efficiency optimization for a sucker-rod pumping system is presented. Our new method combines a slip model of the surface-transmission system (STS) with a closely coupled model of the downhole rod-string vibration to provide an improved method for calculating the motion of a rod string and the power requirements for a conventional sucker-rod pumping system. The new model proposed in this paper will provide an improved prediction of the power requirements for conventional sucker-rod pumping systems, and the results will be significantly improved as the amount of slip in the STS increases. The new model is verified by comparing it with the available analytical solutions, and good agreement is found. Real application in a high-energy-consumption oil field shows that the new model in this paper will result in significant improvements in system design, especially when the oil wells have a small-diameter pump and high stroke frequency.