At PO2 = 40 mm Hg, which statement about the saturation of either myoglobin (Mb) or hemoglobin (Hb) is true? At PO2 = 40 mm Hg, which statement about the saturation of either myoglobin (Mb) or hemoglobin (Hb) is true? At this partial pressure of oxygen, neither Hb nor Mb would be fully saturated with oxygen. At this partial pressure of oxygen, both Hb and Mb would be equally saturated with oxygen. At this partial pressure of oxygen, Mb would be almost completely saturated but Hb would not. At this partial pressure of oxygen, Hb would be completely saturated but Mb would not.