Oil wells drilled horizontally through hydrocarbon-bearing formations are often among the most prolific oil wells in the United States. Although modern horizontal drilling achieved commercial success in the 1980s, drilling techniques have improved, and in recent years, horizontal drilling has become more common.
Geologic formations are almost always much greater in horizontal extent than they are in vertical thickness. For this reason, more oil-bearing rock is exposed for production in horizontal drilling than in vertical drilling. Horizontal wells are often completed in combination with hydraulic fracturing to maximize production along the exposed rock formation.
In 2015 nearly 77% of the most prolific U.S. oil wells, or those producing more than 400 barrels of oil equivalent (BOE) per day, were horizontally drilled wells. For about 85,000 moderate rate wells producing in 2015, defined here as more than 15 BOE per day and up to 400 BOE per day, 42% were drilled horizontally. Of the approximately 370,000 lowest-rate, marginal oil wells in 2015, also known as stripper wells, only about 2% were horizontal wells.