A virtual flow meter, comprising: a processor-based controller configured to: select or receive a selection of an operating point related to a given flow rate of a phase of a production fluid, such as for gas, oil, and/or water in a multiphase context; access sensor data acquired from one or more pressure and temperature sensors, and flow rates of gas, oil, and/or water measured using multiphase flow meters; select or receive a selection of a nominal case comprising the mean values of measured inlet pressure, measured inlet temperature, measured gas mass flow rate, measured oil mass flow rate and measured water mass flow rate based on said received sensor data; based on the operating point and the nominal case, generate a calculated outlet pressure and a calculated outlet temperature at a segment of interest; for each combination of the mean values of measured inlet pressure, measured inlet temperature, measured gas mass flow rate, measured oil mass flow rate, and measured water mass flow rate for said operating point, each mean value being associated with a measurement error obtained for a segment of interest over a time interval: derive an outlet pressure and an outlet temperature at the segment for each combination; characterized by calculate an outlet pressure difference between the calculated outlet pressure for the nominal case and the outlet pressure calculated for each combination; and calculate an outlet temperature difference between the calculated outlet temperature for the nominal case and the outlet temperature calculated for each combination; determine the largest outlet pressure difference and the largest outlet temperature difference for the combinations; and select the largest outlet pressure difference and the largest outlet temperature difference as uncertainties related to, respectively, the outlet pressure and outlet temperature calculated for the nominal case. a processor-based controller configured to: select or receive a selection of an operating point related to a given flow rate of a phase of a production fluid, such as for gas, oil, and/or water in a multiphase context; access sensor data acquired from one or more pressure and temperature sensors, and flow rates of gas, oil, and/or water measured using multiphase flow meters; select or receive a selection of a nominal case comprising the mean values of measured inlet pressure, measured inlet temperature, measured gas mass flow rate, measured oil mass flow rate and measured water mass flow rate based on said received sensor data; based on the operating point and the nominal case, generate a calculated outlet pressure and a calculated outlet temperature at a segment of interest; for each combination of the mean values of measured inlet pressure, measured inlet temperature, measured gas mass flow rate, measured oil mass flow rate, and measured water mass flow rate for said operating point, each mean value being associated with a measurement error obtained for a segment of interest over a time interval: derive an outlet pressure and an outlet temperature at the segment for each combination; characterized by calculate an outlet pressure difference between the calculated outlet pressure for the nominal case and the outlet pressure calculated for each combination; and calculate an outlet temperature difference between the calculated outlet temperature for the nominal case and the outlet temperature calculated for each combination; select or receive a selection of an operating point related to a given flow rate of a phase of a production fluid, such as for gas, oil, and/or water in a multiphase context; access sensor data acquired from one or more pressure and temperature sensors, and flow rates of gas, oil, and/or water measured using multiphase flow meters; select or receive a selection of a nominal case comprising the mean values of measured inlet pressure, measured inlet temperature, measured gas mass flow rate, measured oil mass flow rate and measured water mass flow rate based on said received sensor data; based on the operating point and the nominal case, generate a calculated outlet pressure and a calculated outlet temperature at a segment of interest; for each combination of the mean values of measured inlet pressure, measured inlet temperature, measured gas mass flow rate, measured oil mass flow rate, and measured water mass flow rate for said operating point, each mean value being associated with a measurement error obtained for a segment of interest over a time interval: derive an outlet pressure and an outlet temperature at the segment for each combination; characterized by calculate an outlet pressure difference between the calculated outlet pressure for the nominal case and the outlet pressure calculated for each combination; and calculate an outlet temperature difference between the calculated outlet temperature for the nominal case and the outlet temperature calculated for each combination; determine the largest outlet pressure difference and the largest outlet temperature difference for the combinations; and select the largest outlet pressure difference and the largest outlet temperature difference as uncertainties related to, respectively, the outlet pressure and outlet temperature calculated for the nominal case.