A formation tester for determining the formation pressure of a subsurface formation traversed by a wellbore comprises of:—an elongate tester body;—a support plate (3) that is extendible outwardly from the surface of the formation tester body, said support plate carrying probe means (5) to establish a passageway between the inside of said formation tester body and said formation, and a sealing pad (6) connected to said probe means to isolate said passage way between the inside of said formation tester body and said formation;—anchoring means (7) to settle said tester body at a level within the wellbore. The elongate tester body comprises an eccentric portion (2) wherein said support plate is mounted such that a determined standoff is maintained between said elongate tester body and the wall of the wellbore when said tester body is settled at a level in the wellbore.