There are a number of models for gas lift in the literature, but most of them suffer from large scale simplifications and, hence, unacceptable errors. Those simplifications include ignoring the temperature profile, assuming ideal gas, and neglecting the time- delay between applications of the gas injection pressure on the surface and sensing its effect at point of injection. In this study, all mentioned deficiencies are overcome and a new model is developed for predicting the pressure profile in the annulus and at the injection point. Then using sensitivity analysis, the applicability and accuracy of this model are discussed and compared with earlier models. Results show that the new model yields accurate results and hence serves as an excellent tool for control problems. In addition as by accurate estimation of pressure at the injection point, flow instability can be predicted and prevented, this model can be of great help to prohibit the problem of flow instability.