Abstract This paper presents the laboratory development and a field trial of a novel 100% oil base drilling fluid system. In response to the need for a competitive high temperature inhibitive system, lab testing found an oil soluble polymer that imparts high temperature high pressure fluid loss control in a mud system with stable rheology and low formation damage. The polymeric additive is the basis for the 100% oil system, which also has an application in standard invert emulsion systems. The 100% oil system is designed to use mineral or diesel oil as the base. The attributes of the system include inherent inhibition and lubricity from the base oil, a mud weight range of 7.0–18.0 ppg, minimal formation damage, resistance to contamination and maintenance of the HPHT filtration control and rheology during high temperature high pressure applications. Laboratory testing has shown the fluid is temperature stable to 400 °F with diesel or low toxicity mineral oil as the base. This system has been field tested on two wells in Eastern Venezuela. One test was a 6,353', 8 ½" directional interval and the other a 1,053', 5 7/8" horizontal section drilled in near balance conditions with the fluid being nitrogenated to achieve the desired ECD. Both wells were drilled successfully and one well is discussed in this report. This fluid has a wide range of applications evidenced by the documented properties from the lab and the field tests. This paper covers the system formulations, properties, formation damage tests, and the results from the field test.