In the development of many of today's reservoirs, the oil and gas industry is challenged to drill more efficiently and is asked constantly to maximize recovery and production. However, drilling through these reservoirs is challenging because geologic models often are limited to the resolution of seismic data, and offset wells often have significant variations. Geosteering is the process of adjusting the borehole trajectory in real time to correct for unanticipated variations in geology and structure to avoid exiting the target zone. It is a technique currently used on many horizontal and deviated wells for better well placement and for efficiently draining a reservoir. Recent improvements in well-placement and formation-evaluation technologies have helped in gaining access to bypassed reserves that originally were not thought to be practical targets. Examples highlight the economic benefit of geosteering and well-placement technology. Maximum reservoir contact in the sweet spot leads to increased production, and early warning of approaching faults and bed boundaries results in reduction of sidetracks. Furthermore, keeping the well trajectory away from the oil-water contact optimizes production by producing less water. Finally, maximizing production by placing the wellbore entirely within the best reservoir zone boosts productivity so that wells that previously appeared difficult or uneconomic are now becoming viable.