A multi-stage compressor comprising: a housing ; a stacked rotor comprised of a plurality of segments, the plurality of segments including flanges attached together, wherein one of said flanges is configured to operate as a first balance drum ; a first compressor section including: a first inlet duct configured to conduct process gas into said first compressor section ; a first outlet duct configured to conduct pressurized process gas out of said first compressor section ; at least one first impeller connected to said rotor between said first inlet duct and said first outlet duct ; and wherein said first inlet duct is adapted to permit said first balance drum to be disposed between said first inlet duct and said rotor and a second compressor section including: a second inlet duct configured to conduct process gas into said second compressor section ; a second outlet duct configured to conduct pressurized process gas out of said second compressor section ; at least one second impeller connected to said rotor between said second inlet duct and said second outlet duct ; and a second balance drum connected to said rotor and disposed between said first compressor section and said second compressor section; wherein a first volume of said first inlet duct is greater than a second volume of said second inlet duct. a housing ; a stacked rotor comprised of a plurality of segments, the plurality of segments including flanges attached together, wherein one of said flanges is configured to operate as a first balance drum ; a first compressor section including: a first inlet duct configured to conduct process gas into said first compressor section ; a first outlet duct configured to conduct pressurized process gas out of said first compressor section ; at least one first impeller connected to said rotor between said first inlet duct and said first outlet duct ; and wherein said first inlet duct is adapted to permit said first balance drum to be disposed between said first inlet duct and said rotor and a first inlet duct configured to conduct process gas into said first compressor section ; a first outlet duct configured to conduct pressurized process gas out of said first compressor section ; at least one first impeller connected to said rotor between said first inlet duct and said first outlet duct ; and wherein said first inlet duct is adapted to permit said first balance drum to be disposed between said first inlet duct and said rotor and a second compressor section including: a second inlet duct configured to conduct process gas into said second compressor section ; a second outlet duct configured to conduct pressurized process gas out of said second compressor section ; at least one second impeller connected to said rotor between said second inlet duct and said second outlet duct ; and a second inlet duct configured to conduct process gas into said second compressor section ; a second outlet duct configured to conduct pressurized process gas out of said second compressor section ; at least one second impeller connected to said rotor between said second inlet duct and said second outlet duct ; and a second balance drum connected to said rotor and disposed between said first compressor section and said second compressor section; wherein a first volume of said first inlet duct is greater than a second volume of said second inlet duct. <EOS>