The method of processing air prior to separation of such air into gaseous components, the steps that include: first compressing a stream of air and cooling the compressed air, to enable water separation and removal from the stream, to provide a dry stream of air; then further compressing the dry air stream and cooling the compressed dry air stream to enable removal of contained remanent water; then expanding the cooled air stream in an expansion stage which extracts work from the expanding stream; then passing the expanded air stream to a separator operating to remove water from the stream, thereby producing dry air passed to a component gas separation stage or stages.