A new correlation for the viscosity of ortho-xylene (o-xylene) is presented. The correlation is based upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory. It is applicable in the temperature range from 273 to 673 K at pressures up to 110 MPa. The overall uncertainty of the proposed correlation, estimated as the combined expanded uncertainty with a coverage factor of 2, varies from 1% for the viscosity at atmospheric pressure to 5% for the highest temperatures and pressures of interest. Tables of the viscosity generated by the relevant equations, at selected temperatures and pressures and along the saturation line, are provided.