In recent years, an unusual application of standard integrating sphere has been employed to act as a compact multipass gas absorption cell spectroscopy. This system shows several interests, especially to improve limits of detection thanks to the pressure parameter. In this study, we have modeled the global effects of pressure parameter on absorption measurements. We have tested and compared our simulations by measuring the optical absorption of oxygen under different pressure. The experimental data obtained are in agreement with the simulated results and are discussed in this paper.