The invention relates to a method for liquefying a feed gas or cooling a feed gas at supercritical pressure, in which the feed gas mixed with a cycle gas is condensed or cooled in order to form a supercritical gas or liquid at the first pressure, the liquid at the first pressure is cooled in a first heat exchanger (E2), the cooled liquid is removed from the first exchanger and expanded up to a second pressure that is lower than the first pressure in order to form an expanded flow, at least one portion of the expanded flow is cooled in a second heat exchanger, the expanded flow is removed from the second heat exchanger (E2), said flow is split into at least two portions, including a first portion and a second portion, the first portion of the expanded flow constituting the liquefied product, the second portion and preferably a third portion being vaporized in the second heat exchanger and the thus-formed at least one cycle gas is then mixed with the feed gas and compressed in a compressor, before or after being mixed with the feed gas.