Method for cooling and optionally liquefaction of a product gas, based on a closed loop of multi-component refrigerant with a joined composition of a more volatile fraction and a less volatile fraction, in heat exchange with the gas to be cooled and optionally condensed, the method comprises the steps of: directing the product gas to be cooled through at least one primary two-flow heat exchanger, directing the refrigerant with the joined composition from a first of at least two secondary two-flow heat exchangers through at least one compressor, removing heat absorbed by the refrigerant by heat exchange in one or more heat exchangers, passing the cooled refrigerant into at least one phase-separator for separating the refrigerant into the more volatile fraction and the less volatile fraction, cooling the more volatile fraction in heat exchange with low pressure refrigerant of the joined composition by passing it through the first of the at least two secondary heat exchangers, further cooling the more volatile fraction in heat exchange through the second of at least two secondary two-flow heat exchangers, directing a first part of the further cooled more volatile fraction from the second of at least two secondary heat exchangers to a first throttling device and directing this part into heat exchange in the second of at least two secondary heat exchangers as a first low pressure refrigerant, directing the remaining other part of the further cooled more volatile fraction from the second of the at least two secondary heat exchangers to a second throttling device to become a remaining low pressure refrigerant and directing this part into heat exchange with the product gas to be cooled through the at least one primary heat exchanger, throttling by means of a third throttling device the less volatile fraction from the at least one phase-separator to become a second low pressure refrigerant and directing this less volatile fraction, combined with the remaining low pressure refrigerant from the at least one primary heat exchanger and the first low pressure refrigerant from the second of at least two secondary heat exchangers, into heat exchange and complete vaporization through the first of the at least two secondary heat exchangers, and closing the loop by directing the vaporized refrigerant to the compressor, characterized in that the second low pressure refrigerant with the less volatile fraction, the first low pressure refrigerant with the first part of the more volatile fraction and the remaining low pressure refrigerant with the remaining other part of the more volatile fraction forms the total amount of the joined composition, low pressure refrigerant. directing the product gas to be cooled through at least one primary two-flow heat exchanger, directing the refrigerant with the joined composition from a first of at least two secondary two-flow heat exchangers through at least one compressor, removing heat absorbed by the refrigerant by heat exchange in one or more heat exchangers, passing the cooled refrigerant into at least one phase-separator for separating the refrigerant into the more volatile fraction and the less volatile fraction, cooling the more volatile fraction in heat exchange with low pressure refrigerant of the joined composition by passing it through the first of the at least two secondary heat exchangers, further cooling the more volatile fraction in heat exchange through the second of at least two secondary two-flow heat exchangers, directing a first part of the further cooled more volatile fraction from the second of at least two secondary heat exchangers to a first throttling device and directing this part into heat exchange in the second of at least two secondary heat exchangers as a first low pressure refrigerant, directing the remaining other part of the further cooled more volatile fraction from the second of the at least two secondary heat exchangers to a second throttling device to become a remaining low pressure refrigerant and directing this part into heat exchange with the product gas to be cooled through the at least one primary heat exchanger, throttling by means of a third throttling device the less volatile fraction from the at least one phase-separator to become a second low pressure refrigerant and directing this less volatile fraction, combined with the remaining low pressure refrigerant from the at least one primary heat exchanger and the first low pressure refrigerant from the second of at least two secondary heat exchangers, into heat exchange and complete vaporization through the first of the at least two secondary heat exchangers, and closing the loop by directing the vaporized refrigerant to the compressor, characterized in that the second low pressure refrigerant with the less volatile fraction, the first low pressure refrigerant with the first part of the more volatile fraction and the remaining low pressure refrigerant with the remaining other part of the more volatile fraction forms the total amount of the joined composition, low pressure refrigerant.