Abstract Formation evaluation techniques have been particularly applicable in the Seeligson and Borregos fields because of the widely diversified conditions encountered in the multi-reservoir producing area. Information on the acquisition, utilization, and benefits of formation evaluation data in these fields is presented by this paper. Introduction The Seeligson and Borregos fields are located in close proximity to each other in southeastern Jim Wells and western Kleberg counties, Texas. These fields contain major reserves and have a combined areal extent of approximately65,000 acres. A series of closely related anticlinal structures with fault patterns and changes in lithology, combined with the development of more than 50 sands, results in many individual reservoirs in the two fields. These reservoirs, which range from 4,500 to 7,500 ft in depth, are in the Frio and Vicksburg formations. Reservoir drive mechanisms include dissolved gas, strong gas cap, and water drives. Average reservoir permeabilities range from 150 to 4,000 md. Oil column lengths vary from 4 to 550 ft, and oil gravities range from 30 to 45°API. The purpose of this paper is to describe some of the methods that have been used in the Borregos and Seeligson fields to obtain reservoir information and to employ this information in the determination of optimum producing operations. Acquisition of Formation Evaluation Data Studies of the factors influencing the behavior of individual wells and reservoirs are required to realize maximum profits in the production of oil. To make possible these studies, detailed information is required on the physical properties of a reservoir, together with the occurrence, distribution, and properties of the fluids within the reservoir. This information is regarded as formation evaluation data. Although supplemented by production and subsurface sample pressure data, the majority of reservoir information is obtained from core analyses, well logging, and drill-stem tests. These three methods of obtaining data, which can be considered the standard tools of formation evaluation, have been extensively employed in the Seeligson and Borregos fields.