An analysis was made of three-dimensional steady-state computations for the thermal mixing tests performed in the Oconee 1 pressurized water reactor at the beginning of fuel cycle 6 early in 1980 under the sponsorship of the Electric Power Research Institute. It was found that detailed modeling of the 52 asymmetrically located instrument guide tubes, together with the various structures in the lower plenum, yielded generally good agreement with the data (within 1°F). Most of the thermal mixing trends at the entrance to the core and midplane deduced from the 29-thermocouple reading were correctly computed.