We present a clamped vibrating-wire instrument and the associated methods of measurement and analysis that enabled gas-mixture viscosity measurements at densities up to 110 kg.m(-3) with a standard uncertainty of 0.09 mu Pa.s, which is a relative uncertainty of 0.60 %. The vibrating-wire was clamped at both ends and operated in the steady-state mode to make the apparatus more compact and allow operation over a broad range of conditions. New modifications to the method include an interleaved measurement protocol to minimize errors arising from fluctuations in temperature and pressure, and optimization of the signal-to-noise while ensuring that the driven wire's response remained in the linear regime. The wire's radius was determined from calibration measurements with He, and the viscometer's performance was verified with N-2, CO2, and CH,. The discrepancies between the measured pure fluid viscosities and those predicted with models implemented in the software REFPROP 9.1 were smaller than 1 %; literature data for these fluids exhibit similar deviations. Viscosities of (1 - x)C3H8 + xCH(4) with x = 0.9452, and (1 - x)CO2 + xCH(4) with x = 0.57 were also determined at pressures between (1.5 and 6.5) MPa and temperatures of (280, 303 and 328) K. The largest rms deviation of 3.6 % of the measured viscosities relative to those calculated with the extended corresponding states model implemented in REFPROP occurred for CH4 + CO2 at a temperature of 328 K.