A method and apparatus are provided, comprising an internal combustion engine equipped with a variable geometry intake air compressing device and a control module operative to estimate exhaust gas pressure during ongoing engine operation. The control module is adapted to monitor sensing devices of the internal combustion engine, and is adapted to execute algorithms. The method comprises monitoring signal inputs from the sensing devices, and determining operating parameters for exhaust flow and an exhaust pressure of the intake air compressing device. An exhaust pressure ratio is determined based upon the parameters for exhaust flow and the exhaust pressure of the intake air compressing device. An exhaust pressure is determined based upon the exhaust pressure ratio.