Contents of this course are specifically designed for field and office personnel who will be involved in underbalanced drilling operations. Although underbalanced drilling is not new to the oil industry, underbalanced drilling techniques have recently evolved into more complicated operations. Underbalanced drilling has become more prevalent with the advent of underbalanced drilling in horizontal wells. The course will familiarize the participant with all underbalanced drilling operations including air, mist, foam, gasified fluids, flow drilling, mud cap drilling and snub drilling. The participant will learn the advantages and limitations of each drilling method so the best option for underbalanced drilling in the field can be applied. Included are methods for calculating lifting capacity and volume requirements with example problems and equipment design from the bit to the compressor system. Discussed are some of the potential problems such as downhole fires, stuck pipe, water influx, fishing limitations, mud rings and high production rates.