The invention relates to a method of separating a dry feed gas (1) containing mostly methane, ethane and propane into a first product (17), called the treated gas, which is relatively more volatile, and a second product (34), called fraction C2 plus, which is relatively less volatile. The inventive method comprises: (i) an operation involving the cooling of the supply gas (1) into a cooled gas (2); (ii) an operation whereby the cooled gas (2) from operation (i) is separated and treated; and (iii) distillation in a distillation device (C3). The invention also relates to the corresponding installation. According to the invention, the distillation device (C3) comprises at least first and second distillation columns, (C1) and (C2), which operate at different pressures.