Observations of the average Oxygen ionization equilibrium as a function of speed of the solar wind are presented. At low solar wind speeds they indicate a coronal temperature at the freezing-in point of 1.5¿0.2¿10 ¿K. At speeds above 450 km sec-1 the apparent temperature starts to rise rapidly. This rise is tentatively interpreted in terms of a lack of thermodynamic equilibrium in the source region.