A vibrating wire viscometer has been developed with an electrically insulating tensioning mechanism. It has been used with two wires, one of diameter 0.05 mm the other of diameter 0.15 mm, to measure the viscosity of methylbenzene and two reference fluids with viscosities of (14 and 240) mPa center dot s at T = 298 K and p = 0.1 MPa at temperatures in the range from (298 to 373) K and pressures below 40 MPa, where the viscosity covers the range from (0.3 to 100) mPa center dot s with an uncertainty of < 0.6%. The results so obtained differ from literature values by < 1%. Measurements with the 0.150 mm diameter wire at T 301 K demonstrate that the upper operating viscosity is 200 mPa center dot s with an uncertainty of about 3%.