In the present work, of interest of the oil industry, a methodology was developed for metrological evaluating and determination the frequency of calibration of natural gas flow rate measurement systems with orifice plates, using calibration data obtained every two months from measurement instruments installed in fiscal points of the Campos Basin. The study evaluates the calibration data of temperature, pressure and differential pressure measurement from a multivariable transmitter, contributing to a better understanding of the influence of those variables in the uncertainty of flow rate as a result of the methodological evaluating, the intervals between two successive calibrations was determined, so that the requirements of the Portaria Conjunta n° 1 ANP/INMETRO, 19/06/2000, could be met in the fiscal and allocation points. First of all, it was shown that the flow rate uncertainty values, as calculated by ISO 5167-2 standard was fully covered by the requirements. Finally, it was shown the interval between successive calibrations could be increased of the value nowadays required by portaria (2 months) to 6 months for pressure and differential pressure, and to 14 months for temperature. This results has an economic and operational impact in the natural gas industry.