Method of installing a subsea system comprising the steps of: - installing at least one first foundation structure on a seabed, wherein the first foundation structure comprises a connection interface configured to connect to a second foundation structure (13") configured to at least partly support an additional compressor train on the seabed, and wherein the additional compressor train increases the subsea system capacity when there is a need for it, - installing a first compressor train on the foundation structure, the first compressor train comprising at least a first compressor, - connecting the first compressor train to at least one well flow line, - connecting a first compressed fluid line to an outlet of the first compressor and to a common outlet for the compressed fluid in the subsea system, wherein the first compressed fluid line comprises a flow regulation device, - connecting a first connection line (10', 12') to the first compressed fluid line at a position upstream of the flow regulation device and/or to a line (2', 6') at a position upstream of the first compressor, and wherein the first connection line (10', 12') is configured to connect to the additional compressor train positioned at least partly on the second foundation structure (13"), the first connection line (10', 12') comprising a flow regulation device (20', 22'), - connecting a second connection line to the first compressed fluid line at a position downstream of the flow regulation device and wherein the second connection line is configured to connect to the additional compressor train positioned at least partly on the second foundation structure (13"), the additional compressor train is thereby connectable to the common outlet, the second connection line comprising a flow regulation device. - installing at least one first foundation structure on a seabed, wherein the first foundation structure comprises a connection interface configured to connect to a second foundation structure (13") configured to at least partly support an additional compressor train on the seabed, and wherein the additional compressor train increases the subsea system capacity when there is a need for it, - installing a first compressor train on the foundation structure, the first compressor train comprising at least a first compressor, - connecting the first compressor train to at least one well flow line, - connecting a first compressed fluid line to an outlet of the first compressor and to a common outlet for the compressed fluid in the subsea system, wherein the first compressed fluid line comprises a flow regulation device, - connecting a first connection line (10', 12') to the first compressed fluid line at a position upstream of the flow regulation device and/or to a line (2', 6') at a position upstream of the first compressor, and wherein the first connection line (10', 12') is configured to connect to the additional compressor train positioned at least partly on the second foundation structure (13"), the first connection line (10', 12') comprising a flow regulation device (20', 22'), - connecting a second connection line to the first compressed fluid line at a position downstream of the flow regulation device and wherein the second connection line is configured to connect to the additional compressor train positioned at least partly on the second foundation structure (13"), the additional compressor train is thereby connectable to the common outlet, the second connection line comprising a flow regulation device.