the present invention generally relates to an apparatus and method for sealing a wellbore . in one aspect an apparatus for sealing a wellbore is provided . the apparatus includes a swelling elastomer disposed around an outer surface of the tubular body . the swelling elastomer is isolated from wellbore fluid in an annulus . however , upon the application of an outwardly directed force to an inner surface of the tubular body , the tubular body expands radially outward causing the swelling elastomer to contact the wellbore while exposing the swelling elastomer to an activating agent via the one or more apertures , thereby causing the swelling elastomer to create a pressure energized seal with one or more adjacent surfaces in the wellbore . in another aspect , a liner assembly for isolating a zone in a wellbore is provided . in yet another aspect , a method for sealing a wellbore is provided .