A refrigeration system comprising; a compressor out of which compressed refrigerant gas issues, said refrigerant gas having compressor lubricant entrained within it; a condenser, said condenser condensing refrigerant gas received from said compressor to liquid form; a metering device, said metering device receiving condensed system refrigerant and compressor lubricant from said condenser; an evaporator, said evaporator receiving refrigerant in its gaseous state, refrigerant in its liquid state and compressor lubricant from said metering metering device, said liquid refrigerant being distributed within said evaporator to promote the transfer of heat from a heat transfer medium flowing through said evaporator to said refrigerant, a first portion of said refrigerant received in said evaporator in its liquid state being vaporized within said evaporator by heat exchange contact with said heat transfer medium and a second portion of said refrigerant received in said evaporator in its liquid state, together with compressor lubricant, pooling in the lower portion of said evaporator as a mixture of liquid refrigerant and compressor lubricant; and means for returning said mixture to a different location in said evaporator, from where said returned mixture is re-distributed for heat transfer with said heat transfer medium flowing through said evaporator, by exposing said mixture to a pressure higher than evaporator pressure, characterized in that said means for returning includes a collection tank, said mixture passing from said evaporator into said collection tank prior to its return to said location in said evaporator, the mixture returned to said location in said evaporator for re-distribution therein being returned from said collection tank. a compressor out of which compressed refrigerant gas issues, said refrigerant gas having compressor lubricant entrained within it; a condenser, said condenser condensing refrigerant gas received from said compressor to liquid form; a metering device, said metering device receiving condensed system refrigerant and compressor lubricant from said condenser; an evaporator, said evaporator receiving refrigerant in its gaseous state, refrigerant in its liquid state and compressor lubricant from said metering metering device, said liquid refrigerant being distributed within said evaporator to promote the transfer of heat from a heat transfer medium flowing through said evaporator to said refrigerant, a first portion of said refrigerant received in said evaporator in its liquid state being vaporized within said evaporator by heat exchange contact with said heat transfer medium and a second portion of said refrigerant received in said evaporator in its liquid state, together with compressor lubricant, pooling in the lower portion of said evaporator as a mixture of liquid refrigerant and compressor lubricant; and means for returning said mixture to a different location in said evaporator, from where said returned mixture is re-distributed for heat transfer with said heat transfer medium flowing through said evaporator, by exposing said mixture to a pressure higher than evaporator pressure, characterized in that said means for returning includes a collection tank, said mixture passing from said evaporator into said collection tank prior to its return to said location in said evaporator, the mixture returned to said location in said evaporator for re-distribution therein being returned from said collection tank.