We have used the Siggaard-Andersen algorithm for oxygen parameters to develop a Fortran 4.1 program which calculates the concentration of oxygen released from arterial blood when the pO2 is reduced to a stated value. This program can be used to generate the in vivo oxygen dissociation curve. Substitution of 4.0 kPa allows calculation of the concentration of oxygen released from arterial blood when the blood becomes venous at a pO2 of 4.0 kPa. This entity is an estimate of the maximal amount of oxygen available for release from arterial blood. We have termed it "Maximal Available Oxygen". We believe that "Maximal Available Oxygen" is a simpler concept to describe oxygen carriage and release properties of blood than "Uncompensated Mixed Venous Oxygen Tension" and "Cardiac Oxygen Compensation Factor", and possesses a number of other theoretical and practical advantages. The algorithm is unsuitable when arterial blood is highly saturated with oxygen. To overcome this problem, we have modified the algorithm to allow generation of the curve and estimation of "Maximal Available Oxygen" and other parameters from a specimen of arterial and a specimen of venous blood.