(Übertragungsnetzbetreiber, ÜBN) In Germany, the maximum voltage transmission grid is largely owned by the four transmission system operators (TSOs) - TenneT, 50Hertz, Amprion, and TransnetBW - which are responsible for the operation, maintenance, and development of their respective sections of the German grid. It is their job to regulate power supply, including balancing fluctuating power from renewables with more predictable conventional generation (see→ re-dispatch costs). Since each TSO runs the grid within its control area, they are natural monopolies. In Germany, TSOs were integrated into larger utilities, until EU regulation called for the unbundling of grid and energy supply/generation.