This paper deals with the comparison of gas and oil standard pressure system up to 7 MPa using pressure calibrator as a portable standard. This comparison was carried out using the systems placed in Laboratory for thermal measurements at Faculty of Mechanical Engineering and Naval Architecture. Theoretical bases in pressure measurements are shown in the opening chapters, focusing on piston gauges. After the theoretical bases, mathematical models for effective pressure calculations are given for both gas and oil standard pressure system. Calculation methods for measurement uncertainties and statistical methods for calibration feedback which are used in result analysis are also shown in this chapter. Measurement facilites have been described and the characteristics of the equipment used for calibration are given. The operating principle and measurement procedure are also explained in this chapter. The result analysis, as the main part of this thesis, has been conducted using mathematical models and procedures described in the opening chapters. Mass sets characteristics used for calibration are given and effective pressures and measure uncertainties are calculated, for all measure points in both gas and oil standard pressure system. The main indicator for the comparison of mentioned standard pressure systems is the divergence in system deviation. The analysis of the obtained deviation gave an overview of the current state of standard pressure systems used in a laboratory and, based on those results, further steps for improving the above-described systems are proposed. The main goal of the described calibration was the internal quality control for pressure standards used in Laboratory for thermal measurements.