What is the oxygen content at 30000 feet?

In terms of percentage content, it's almost exactly what it would be at sea level, around 20/21%.

Of course, the density of the atmosphere is far lower, so whereas you'd have around 15PSI at sea level, at 30,000 feet it'd be down around 4PSI or lower. Answer Just like above, but I would like to say not enought to sestain life. That is why you need to pressurize and aircraft