Refrigeration cycle, comprising at least one lower suction pressure compressor, at least one higher suction pressure compressor, the at least one lower suction pressure compressor and the at least one higher suction pressure compressor connected in series, a heat-rejection heat exchanger, preferably a collecting container, at least one lower suction pressure evaporator having an expansion device connected upstream thereof, at least one higher suction pressure evaporator having an expansion device connected upstream thereof and conduits circulating a refrigerant therethrough, wherein the at least one lower suction pressure compressor comprises: an inlet port, a compression element, an outlet port, wherein in operation a refrigerant flow of a gaseous refrigerant carrying an amount of oil circulates through the inlet port, the compression element and the outlet port, an oil sump in which part of the oil carried by the gaseous refrigerant collects, characterized in that the at least one lower suction pressure compressor further comprises an oil circulation rate enhancement feature configured so as to direct oil from the oil sump to the refrigerant flow and thus to the higher suction pressure compressor connected downstream, when the oil in the oil sump exceeds a predetermined oil sump level; in that the lower suction pressure compressor and the higher suction pressure compressor are configured such that when the oil sump level of the lower suction pressure compressor is less than its predetermined oil sump level, its oil circulation rate is always lower than the oil circulation rate of the higher suction pressure compressor; and in that the lower suction pressure compressor and the higher suction pressure compressor are configured such that when the oil sump level of the lower suction pressure compressor exceeds its predetermined oil sump level, its oil circulation rate is always higher than the oil circulation rate of the higher suction pressure compressor. an inlet port, a compression element, an outlet port, wherein in operation a refrigerant flow of a gaseous refrigerant carrying an amount of oil circulates through the inlet port, the compression element and the outlet port, an oil sump in which part of the oil carried by the gaseous refrigerant collects, characterized in that the at least one lower suction pressure compressor further comprises an oil circulation rate enhancement feature configured so as to direct oil from the oil sump to the refrigerant flow and thus to the higher suction pressure compressor connected downstream, when the oil in the oil sump exceeds a predetermined oil sump level; in that the lower suction pressure compressor and the higher suction pressure compressor are configured such that when the oil sump level of the lower suction pressure compressor is less than its predetermined oil sump level, its oil circulation rate is always lower than the oil circulation rate of the higher suction pressure compressor; and in that the lower suction pressure compressor and the higher suction pressure compressor are configured such that when the oil sump level of the lower suction pressure compressor exceeds its predetermined oil sump level, its oil circulation rate is always higher than the oil circulation rate of the higher suction pressure compressor.