A screw compressor comprising: a compressor housing; a compression chamber extending between first and second ends of the housing; an inlet port upstream of the compression chamber; a discharge port downstream of the compression chamber; male and female screw rotors (112, 114) rotatably meshed together within the compression chamber, the screw rotors operable for compressing a working fluid; a compression pocket defined by a region in the compression chamber that is sealed from the inlet port and the discharge port; a first lubricant injection port configured to inject lubricant into the compression chamber at a first volume ratio; a second lubricant injection port configured to inject lubricant into the compression chamber at the first volume ratio; a third lubricant injection port configured to inject lubricant into the compression chamber at a second volume ratio, wherein the second volume ratio is less than the first volume ratio; and a fourth lubricant injection port configured to inject lubricant into the compression chamber at the second volume ratio; characterised in that the screw compressor further comprises: a main lubricant gallery formed in the compressor housing and a main lubricant inlet connected to the main lubricant gallery, the main lubricant inlet in fluid communication with a source of lubricant; and first and second axial lubricant galleries (150, 154) extending from the main lubricant gallery; wherein the first and second injection ports (122, 124) extend directly from the main lubricant gallery; wherein the third and fourth injection ports (152, 156) extend from a distal end of the first and second axial lubricant galleries (150, 154), respectively; and wherein the first, second, third and fourth lubricant injection ports (122, 124; 152, 156) each define a passageway from the main lubricant gallery into the compression chamber to direct lubricant from the main lubricant inlet into the compression chamber. a compressor housing; a compression chamber extending between first and second ends of the housing; an inlet port upstream of the compression chamber; a discharge port downstream of the compression chamber; male and female screw rotors (112, 114) rotatably meshed together within the compression chamber, the screw rotors operable for compressing a working fluid; a compression pocket defined by a region in the compression chamber that is sealed from the inlet port and the discharge port; a first lubricant injection port configured to inject lubricant into the compression chamber at a first volume ratio; a second lubricant injection port configured to inject lubricant into the compression chamber at the first volume ratio; a third lubricant injection port configured to inject lubricant into the compression chamber at a second volume ratio, wherein the second volume ratio is less than the first volume ratio; and a fourth lubricant injection port configured to inject lubricant into the compression chamber at the second volume ratio; characterised in that the screw compressor further comprises: a main lubricant gallery formed in the compressor housing and a main lubricant inlet connected to the main lubricant gallery, the main lubricant inlet in fluid communication with a source of lubricant; and first and second axial lubricant galleries (150, 154) extending from the main lubricant gallery; wherein the first and second injection ports (122, 124) extend directly from the main lubricant gallery; wherein the third and fourth injection ports (152, 156) extend from a distal end of the first and second axial lubricant galleries (150, 154), respectively; and wherein the first, second, third and fourth lubricant injection ports (122, 124; 152, 156) each define a passageway from the main lubricant gallery into the compression chamber to direct lubricant from the main lubricant inlet into the compression chamber. a main lubricant gallery formed in the compressor housing and a main lubricant inlet connected to the main lubricant gallery, the main lubricant inlet in fluid communication with a source of lubricant; and first and second axial lubricant galleries (150, 154) extending from the main lubricant gallery; wherein the first and second injection ports (122, 124) extend directly from the main lubricant gallery; wherein the third and fourth injection ports (152, 156) extend from a distal end of the first and second axial lubricant galleries (150, 154), respectively; and wherein the first, second, third and fourth lubricant injection ports (122, 124; 152, 156) each define a passageway from the main lubricant gallery into the compression chamber to direct lubricant from the main lubricant inlet into the compression chamber.