For the national gas transmission system to operate in a stable and reliable manner, the entry gas and exit gas should be more or less in balance. This so-called balancing regime is aimed at a system in which each individual shipper ensures that the entry gas and the exit gas within his portfolio are balanced. A time shift standard of two hours will apply here between gas realized at the entry point and gas realized at the exit point. This time delay is the result of the buffer effect of the transmission grid: a change in the exit time is absorbed in the first instance by the grid; the entry should be adjusted to reflect this change shortly thereafter. This means that the required balance will be achieved when, within a portfolio, the difference between the sum of the realizations at the exit points during hour t (for example 08:00 hrs – 9:00 hrs) and the sum of the realization at the entry points during hour t+2 (in this example: 10:00 hrs – 11:00 hrs) lies within the allowed tolerance limits. When the hourly difference exceeds the hourly tolerance, this will be considered an hourly imbalance. When the aggregate hourly differences exceed the cumulative tolerance, this will be considered a cumulative imbalance. When the cumulative hourly difference at the end of the gas day exceeds the daily margin, this will be considered a daily imbalance.