A method of compressing a gas, which uses a compressor train having a plurality of discrete portions and including at least an upstream portion, a mid-stream portion and a downstream portion arranged successively in flow series. The method includes: (i) performing a first compression step by directing a flow of said gas into the upstream compressor portion and driving the upstream compressor portion to compress the gas; (ii) performing a second compression step by directing the compressed flow from the upstream compressor portion into the mid-stream compressor portion and driving the mid-stream compressor portion to further compress the gas; and (iii) performing a third compression step by directing the compressed flow from the mid-stream compressor portion into the downstream compressor portion and driving the downstream compressor portion to further compress the gas.