The present study aims at developing a simple, robust, and reliable equation of state (EOS) for pure fluids and their mixtures. It is demonstrated that the temperature dependencies attached to the parameters of the existing engineering EOS models, and which may result in nonphysical predictions, can be replaced by the slight improvement of the theoretical base. The novel approach not only keeps the EOS model simple but also removes the need for the tedious fitting of the temperature-dependent parameters. In addition, it is free of numerical pitfalls and demonstrates a surprising reliability in predicting different thermodynamic properties in a wide range of temperatures and pressures. The new EOS could be a good starting point for further development.