We present a numerical-experimental diffusion study in which we elucidate the spatial oxygen profile around and inside a zebra fish embryo in the pre-circulation stage (24-28 hpf). Lowest oxygen partial pressures are found in the head with a gradient of posteriorly increasing pressure along the midline of the embryo. Furthermore, this study shows the yolk mass to have a relatively high oxygen permeability as compared to the surrounding medium and the respiring tissue. The oxygen permeability of the respiring tissue in this stage is close to that of water. Knowledge of the details of the oxygen distribution are important for an understanding of vasculogenesis and angiogenesis, since oxygen levels influence the expression of endothelial growth factors.