Summary Hydraulic fracturing is widely used within the petroleum industry to stimulate production rates of wells. The effectiveness of these stimulation treatments depends on the selection of the proper materials to maximize the stimulation effect. Once proper materials are selected, use of substandard materials on site in the hydraulic fracture treatment can reduce the effectiveness of the treatment. We developed a procedure for field monitoring and for evaluating the quality of the materials used in stimulation treatments. The program consists of on-site quality-control checks for water quality, gelled fracturing fluids, proppants, and other additives commonly used in stimulation treatments. A field kit and manual support the program. Often, these on-site quality-control procedures reveal deficiencies that were corrected before a treatment was initiated. If these deficiencies had not been corrected, the treatments may have prematurely terminated and/or the stimulation that resulted from the prematurely terminated and/or the stimulation that resulted from the treatment may have been diminished. Introduction An analysis of service company charges for acidizing and fracturing treatments performed in 1983 indicated that bidding resulted in a 39% savings in the cost of stimulation treatments when compared with list prices. Realization of the magnitude of savings achieved from bidding generated some concern regarding the quality of the product being delivered to location. Chevron's West Texas Div. product being delivered to location. Chevron's West Texas Div. requested and funded the development of a fracturing quality-control program with an overall goal to achieve savings through bidding program with an overall goal to achieve savings through bidding without sacrificing quality. Our well stimulation treatments are generally designed by production engineers. Service companies are then asked to bid on the production engineers. Service companies are then asked to bid on the treatments based on these designs. This process of developing our own treatment designs significantly improved results of stimulation treatments and allowed uniform bidding by service companies. Each service company bids on the same type and amounts of fluids, proppants, hydraulic horsepower, etc. proppants, hydraulic horsepower, etc. To remove further bias from the bidding process and to ensure that a satisfactory product is delivered at the well site, a quality-control program was developed. The objectives of this quality control program areto maximize the productivities of wells that are stimulated,to inform the service companies of management's interest in obtaining quality service and materials,to evaluate service companies fairly so that substandard performance can be eliminated and superior performance encouraged,to obtain feedback from the service companies on how to improve quality of well treatments, andto increase our knowledge of the fracturing process. A viable quality-control program requires adequate evaluation of all stages involved in the treatment. For fracturing treatments, this often begins with the primary cementing program and can include openhole logging, perforating, perforation breakdown, fracturing-fluid tank inspection, water-source evaluation, proppant supplier evaluation, proppant evaluation on location, and evaluation of the service company equipment and personnel performance during the treatment. The cementing, openhole logging, and perforating programs are beyond the scope of this paper. Proper quality control requires an additional engineer whose sole responsibility is to monitor materials, equipment, and personnel performance for the entire job. The effort to obtain improved quality performance for the entire job. The effort to obtain improved quality increases treatment costs, but these costs are usually insignificant compared with the increased productivities of the wells over their producing lives. By having an engineer with the quality-control producing lives. By having an engineer with the quality-control re-sponsibility on location, the other engineer monitoring the job is free to evaluate pressure and rate responses during the job properly and to make any changes in the job procedure dictated by the formation's behavior during the fracturing process. Quality control is a cooperative effort between the service company and the production company designed to improve continually or to upgrade the stimulation service provided on location. Through this cooperative effort, problems can be identified and solutions formulated to enhance overall stimulation success.