Method for low-temperature air separation, in which an air separation unit having a first rectification column and a second rectification column is used, - the first rectification column being operated at a pressure level of 9 to 13.5 bar and the second rectification column being operated at a pressure level of 5.5 to 8.5 bar, - the first rectification column being supplied with cooled compressed air and the second rectification column being supplied with liquid from the first rectification column or liquid formed therefrom, - by means of a first condenser evaporator, head gas of the first rectification column being condensed and liquid from the second rectification column or liquid formed therefrom being evaporated to obtain a first evaporation product, - by means of a second condenser evaporator, head gas of the second rectification column being condensed and further liquid from the second rectification column or liquid formed therefrom being evaporated to obtain a second evaporation product, - by means of a decompression machine, a first portion of the second evaporation product being decompressed, heated and removed from the method, and - head gas of the first rectification column being removed from the method as a pure nitrogen product, - a third rectification column being used, - by means of a third condenser evaporator, sump liquid of the third rectification column or liquid formed therefrom being evaporated to obtain a third evaporation product, and - the third rectification column being supplied with non-evaporated further liquid from the second rectification column or liquid formed therefrom, characterized in that - the third rectification column is operated at a pressure level of 1.1 to 2.5 bar, - a second portion of the second evaporation product is condensed by means of the third condenser evaporator and at least part is supplied into the third rectification column, and in that - further sump liquid of the third rectification column or liquid formed therefrom is internally compressed and removed from the method as an impure oxygen product. - the first rectification column being operated at a pressure level of 9 to 13.5 bar and the second rectification column being operated at a pressure level of 5.5 to 8.5 bar, - the first rectification column being supplied with cooled compressed air and the second rectification column being supplied with liquid from the first rectification column or liquid formed therefrom, - by means of a first condenser evaporator, head gas of the first rectification column being condensed and liquid from the second rectification column or liquid formed therefrom being evaporated to obtain a first evaporation product, - by means of a second condenser evaporator, head gas of the second rectification column being condensed and further liquid from the second rectification column or liquid formed therefrom being evaporated to obtain a second evaporation product, - by means of a decompression machine, a first portion of the second evaporation product being decompressed, heated and removed from the method, and - head gas of the first rectification column being removed from the method as a pure nitrogen product, - a third rectification column being used, - by means of a third condenser evaporator, sump liquid of the third rectification column or liquid formed therefrom being evaporated to obtain a third evaporation product, and - the third rectification column being supplied with non-evaporated further liquid from the second rectification column or liquid formed therefrom, characterized in that - the third rectification column is operated at a pressure level of 1.1 to 2.5 bar, - a second portion of the second evaporation product is condensed by means of the third condenser evaporator and at least part is supplied into the third rectification column, and in that - further sump liquid of the third rectification column or liquid formed therefrom is internally compressed and removed from the method as an impure oxygen product.