An extensive programme of vane testing has been carried out in a peat bog at Escuminac, N.B. to assess the applicability of vane testing to peat. The variables involved in the programme were depth, size of vane, method of insertion, rate of rotation of the vane, and state of peat tested. Vane strength profiles were obtained in a 7 m thick deposit consisting of sphagnum peat (0–4 m), sphagnum carex peat (4–6 m), and carex sphagnum peat (6–7 m). Vane tests were also carried out in the sphagnum peat under anchored Plexiglas sheets to observe the mode of deformation and failure and to measure the movement of markers inserted into the face of the peat. Additional tests were carried out with field vanes in confined sphagnum peat samples in the laboratory.The observed failure surface was essentially cylindrical for all sizes of vane used, but its diameter was consistently 7–10 mm greater than that of the vane for all vane sizes. The sphagnum peat failed at true angles of rotation of between 17 and 40°, leaving a void behind each blade. At maximum torque the peat within each sector started to move monolithically.The moderately decomposed sphagnum moss peat tested is typically neither fibrous nor amorphous, although some fibres and amorphous material are generally present as a result of varying growth and degradation processes. This type of peat could be considered representative of most moss peats with respect to geotechnical behaviour. It is not, however, representative of the less common, truly fibrous sedge peats or of any purely amorphous peat deposits.Analyses of the mode of deformation of the sphagnum peat in vane shear and comparisons with modes of deformation in other types of shear have led the author to conclude that the vane test, in spite of its practical advantages, does not serve any useful purpose in the testing of peat.