Previous rheological studies of water-based muds (WBM＇s) and oil-based muds (OBM＇s) concentrated on fluid viscosities at elevated temperatures and pressures. To evaluate the impact of cold-temperature rheology on the equivalent-circulating-density (ECD) calculations in deepwater webs, three objectives were set for the present study. Extend the available rheological data for the most common drilling-fluid systems to low-temperature environments. Examine the rheograms and determine the best model to fit the data. Evaluate the effect of low-temperature drilling-fluid rheology on the ECD for deepwater applications.