Abstract: Disclosed are container testing apparatuses and methods for detecting leaks in containers. Such employ first and second annular seals for defining a testing chamber therebetween. An actuating seal is shown which is controllably retracted from engagement with sidewalls of the container. Another embodiment uses two passive seals. A further embodiment uses a pressurized expandable seal. In a preferred apparatus and method, at least one of the first and second seals functions by inwardly pressing against the container surfaces to enhance sealing upon application of differentially pressurized fluid within the testing fluid chamber. A detector can be employed to sense changes in the container associated with the existence of a leak through which the differential pressure of the testing fluid is communicated.