Nonisothermal adsorption equilibrium data are described using the virial equation written as a polynomial function in adsorbed-phase loading and reciprocal temperature. This equation is written in terms of polynomials that are orthogonal to summation. As a result, application of the least-squares method to correlate experimental data becomes straightforward and simple, not even requiring any matrix algebra. Ill-conditioning of the normal equations for high-order polynomials is avoided. The model is successfully applied to describe nonisothermal data for different systems over a wide range of temperature and pressure.