We present three models for magma budget during steady-state volcanic activity, by which non-erupted magma is emplaced as dykes or cumulates or crystallises in place. Using gas and thermal data we apply our models at Vulcano to calculate degassing, cooling and crystallisation of magma at a rate of 40--375 kg s-1 within a magma body with an upper surface at a ~2 km depth. At Stromboli we calculate a steady magma supply of 300--1300 kg s-1 to shallow (<1 km) depths. ¿ 1997 American Geophysical Union