The measurement of natural gas by the ultrasonic principle is shown to be competitive in several aspects when compared with orifice plate meters. This paper presents a technical evaluation of the use of multipath ultrasonic meters for custody transfer. The analysis of the meter performance matching with the requirements of principal international standards for measuring of natural gas flowrate by the ultrasonic principle is made using data collected for the same meter during the calibration in laboratory and during operation in the field. It also presents an analysis of the diagnostic tools available by the meter, comparing the results obtained in laboratory and field. A methodology for determining estimates of measurement uncertainty of flow rate and totalize gas in a given time interval is proposed. Evaluations of compliance with the standards and the analysis of the diagnostic tools available show that the use of ultrasonic meters in the fiscal measurement of natural gas is technically feasible, and that, by varying the time for measuring volumes, the uncertainty of measurement can be quite reduced.