Abstract: This invention relates to a single screw compressor comprising a body housing a spindle, a screw and two pinions for engaging the screw, wherein both said pinions and said screw have unequal-width teeth, the diameter along said screw in an outer profile is varied, and the range of the closing angle formed when one of said pinion teeth engages,, with and is in close contact with one of the grooves of said screw is from 60° to 66°. The compressor according to the present invention has advantages such as high gas discharge volume, high Energy Efficiency Ratio, smallbulk, high rigidity with the pinion stand and durability.