Lubricant for a helium compressor requires not only lubrication but also few evolving rate of impurities, because helium refrigerators should be operated stably and continuously for a long time. In this investigation, evolving gases of different types of lubricant were measured to pay attention to heatproof and evolving gases at present operating compressors. It was found that specially refined mineral oil was suitable at the point of heatproof and economy as lubricant for a helium compressor.
