Abstract Field data have been collected and analyzed to 1) identify the characteristics of a drilling fluid that enhance rate of penetration, and 2) quantify the impact of particular fluid properties on rate of penetration. The information is being used to evaluate the economics of a fluid treatment program in order to deliver optimal drilling performance and minimum drilling cost, rather than minimum fluid cost. Additionally, it is demonstrated how bit hydraulics can be improved through rheological modification without adjusting flow rate or nozzle size.