Points out that while all refrigerant and lubricant manufacturers insist that mineral oil (MO) be removed and replaced by polyol ester when changing from R12, R22 or R502 to a pure HFC refrigerant or mixture of HFCs, many compressor manufacturers are investigating the use of mineral oils with HFC refrigerants. Describes the retrofit process recommended by one company. Notes worthwhile reasons for retaining the mineral oil - better lubricity, much reduced solubility for moisture, much lower chemical reactivity, reduced dirt transfer, no suction reed sticking, reduced crankcase oil dilution, lower cost and simple replacement procedure. Concludes that enough evidence exists that retrofits to HFCs, made without changing the oil, can be successful. In many cases, the advantages of MO retention outweigh the minimum risks.