Abstract: A fluid pipeline sampler is disclosed which operates so as to trap a liquid sample and then eject it. To achieve this, a piston (18) and sleeve (14) within a casing (1) are displaced together downwardly to move a pair of portholes (10, 11) in the sleeve out of register with a pair of ports (2, 3) in the casing wall, so as to trap the liquid sample in an internal space between the two portholes (10, 11). In this position the sleeve (14) is restrained against further downward movement. On continuing downward advancement of the piston, the trapped liquid sample is ejected out of the internal space through a passageway (21) in the piston for analysis.