The Gibbs phase rule and thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of temperatures; the concentrations in the absorber and the generator and hence the flow ratios are fixed. For any particular working pair, the coefficient of performance is related to the flow ratio. Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpy-based coefficients of performance have been presented for monomethylamine-water absorption systems for heating. The interaction of operating temperatures have been illustrated graphically.