Liquid oxygen evaporates on a little bit higher temperature than the liquid nitrogen because they both have similar attraction between molecules. It means that different from the normal one, the liquid machine makes less liquid oxygen as a part of it evaporates as a gas.
Explanation:
Liquid oxygen, however, occupies less space as gas, and it makes it lighter for carrying. Also, it can be kept under lower pressure. This is how the liquid oxygen tanks are safer than the tanks with concentrated oxygen that are under high pressure.
