A portion of recent field development efforts in the Hugoton embayment of western Kansas has focused on deeper, less drilled, Mississippian sandstone reservoirs of the Chesterian Series. Such efforts have yielded particular successes in the case of South Eubank field, Haskell County, Kansas. New core data, combined with subsurface mapping and three-dimensional (3-D) seismic information, have led to over 30 new producers being drilled in this field. Reservoirs are best developed in fine-grained, well-sorted, Chesterian sandstones filling a narrow incised paleovalley system that runs north-south through the field. Although new core information contributed to improved reservoir characterization in the area, 3-D seismic data were required to accurately delineate the paleovalley system and thus locate specific prospects. A number of such prospects remain to be drilled. Success at South Eubank suggests that other portions of the same valley system also might be similarly developed. This system extends at least 50 mi (80 km) from northern Haskell County to the Oklahoma border, through a number of existing field areas.