Cubic equations of state (EOSs) are simple and easy at calculation. One way of improving the accuracy of a cubic EOS is through the modification of temperature-dependent energy parameter by using alpha-function. The industrial applications of natural gas are very wide and as a result, prediction of thermodynamic properties and phase behavior of natural gas is an important part of design for such processes. In this work we develop a new a-function for the Peng-Robinson (PR) EOS with the parameters optimized especially for natural gas components. The parameters are generalized as a linear function of acentric factor. The results are compared to the predictions from original PR EOS and other a-functions in literature. It is shown that the new a-function presents a good accuracy with the average deviation of 1.42% for natural gas components.