The viscosity model recently developed for the fully liquid system SiO2-Al2O3-CaO-MgO-Na2O-K2O is further extended to describe the viscosity of the iron oxide containing low order systems in the Newtonian range. The different structural roles of Fe2+ and Fe3+ to the viscosity are captured by the associate species. Using the monomeric associate species in combination with some specific larger structrual units, the model is capable of describing the viscosity of the melts FeO, FeO-SiO2, FeO-Al2PO3, Fe2O3-CaO, Fe2O3-MgO, Fe2O3-Na2O, and Fe2O3-K2O over the whole range of compositions as well as a wide range of temperatures and oxygen partial pressures using only one set of model parameters. A new mechanism is proposed to describe the local viscosity maximum around the fayalite composition in the FeO-SiO2 melt. The model shows that the presence of the local viscosity maximum is dependent on the temperature and oxygen partial pressure. Moreover, the viscosity maximum caused by Al3+ - or Fe3+-induced charge compensation is presented and a good agreement between the calculated viscosities and experimental data is demonstrated.