This paper presents a new and practical methodology to identify the flow units in a mappable geological formation. This approach uses Interwell Flow Capacity Index (IFCI) to describe the flow unit. IFCI is defined as the ratio of actual flow rates (production or injection) in any two wells in a producing unit, with the higher fluid flow rate of the two wells in the denominator. The presented approach uses core, log and production-injection data to describe the variations in reservoir connectivity. The flow units are identified and described by the use of IFCI1 . A flow unit is identified by the similarities between IFCI's calculated by using petrophysical and production-injection data. A Colombian (South America) sandstone, La Cira Field "C1C unit", is used to illustrate the application of IFCI to identify and describe flow units.