Abstract: A blood gas control liquid comprises a stable oil-in-water emulsion that has an oxygen solubility coefficient of at least 10 ml O.sub.2 per 100 ml emulsion and a viscosity of less than 10 centipoises. The emulsion includes water, 5-40 percent by volume of a water-insoluble non-protein compound material, 0.25-10 percent by volume of a nonionic surfactant, a pH buffering agent and a preservative agent which is substantially non-reactive with the pH buffering agent. A preferred blood gas control liquid has a density of about 1.08. The blood gas control liquid has a pH in the range of 7-8, a partial pressure of carbon dioxide in the range of 15-80 millimeters Hg, and a partial pressure of oxygen in the range of 20-600 mm Hg.