Abstract: Disclosed is a for forming a container with multiple walls by blow molding or stretch blow molding of a preform, including a blow-molding phase followed by a degassing phase, beginning at a moment, of the formed container, to bring t:s pressure back to the ambient pressure. The method also includes: a continuous measurement of the pressure prevailing in the neck during the degassing phase; the determination of the length of time that has elapsed between the beginning of the degassing and the attaining of a reference pressure in the neck; the comparison of the length of time that has elapsed with a theoretical length of time that is necessary so that the reference pressure is attained in the neck; and maintaining the locking of the mold if the length of time that has elapsed is less than the theoretical length of time.