There is a need for accurate measurement of hydrogen dispensed into the hydrogen vehicle. This is a very important measurement as it will allow the refuelling station operator to calculate the amount of hydrogen displaced into the vehicle to provide an accurate cost to the customer. No methodology currently exists for calibrating flow meters for hydrogen provided by refuelling stations (up to 875 bar and temperatures between -40oC and 85oC). OIML R 139-1 provides guidelines for the accuracy and approach for testing flow meters at refuelling stations, but due to the lack of experience with metering hydrogen at challenging refuelling conditions, no existing primary standard or verified method is available. Furthermore, due to hydrogen presenting very different characteristics compared to other gaseous fuels, OIML R 139-1 cannot be used for hydrogen as it is and a revision will be needed. Until these methods are developed there will be no traceability for hydrogen metering and thus no legal metrological control of hydrogen dispensers; this means that customers cannot be correctly charged and it is very likely that each station will have no real judgement of how much hydrogen they are dispensing.