Recent progress in oxygen gas sensors based on the EMF method is reviewed. This includes : (a) a multichannel oxygen analyzer; (b) the use of this sensor in the medical field for energy expenditure determination; (c) the effect of temperature gradients in the presence of reactive gases on the relevance of the reading of oxygen-pressure sensors; (d) doubly protected electrochemical cell for accurate, lengthy, coulometric titration, EMF and thermodynamic measurements; and (e) potentiometric sensors based on mixed ionic electronic conductors.