The low temperature emission properties of Ba-dispenser cathodes with different metal and metal+oxide top layers were determined as a function of anode voltage and operating time. A "Sc"/Re-I cathode showed room temperature emission, which was nearly four magnitudes larger than for a W-I cathode. At 300 degrees C, thermionic and field emission were both found superimposed. A Fowler-Nordheim fit derived a remarkable low field emission threshold of 3-4 V/mu m. Nevertheless, emission degradation with time was observed due to oxidation of the Ba-O dipoles. At temperatures below 600 degrees C, oxygen adsorption time constants could be lesser than time constants for desorption of oxygen and resupply the Ba due to oxygen induced desorption, which led to a continuous degradation of emission current. Using oxygen desorption energies and energies required for the Ba resupply (determined from high temperature measurements), we could estimate boundary condition for stable long-term emission. Above 600 degrees C, required low background pressures in the order of 10(-8) mbar are easily obtained. However, at temperatures below 200 degrees C, stable long-term emission will only be possible at very low total background pressures of at least 10(-13) mbar.