The presence of gravel and cobble during Horizontal Directional Drilling (HDD) operations is one of the most challenging situations encountered by contractors. An unexpected encounter with this soil condition often results in difficultly or even failure in completing the bore. This paper presents the results of field research in which three 61 meters installations of 100 mm High Density Polyethylene pipe were performed in gravel/cobble conditions. Each of the bores were completed using various combinations of drilling fluids to demonstrate the effectiveness of using fibres in increasing the chances of success. The first installation was completed using a traditional bentonite/polymer drilling fluid mixture, while the second and third installations were performed with fibre additives mixed into the drilling fluid. The results demonstrated that increased productivity and flow of returns could be achieved with proper drilling fluid considerations. The results of this research should assist HDD contractors in improving the success rate of installations in gravel/cobble conditions.