The paper presents a method for the assessment of standing volume in extensive forest inventories. Information obtained from Landsat-TM-data, Colour Infra-Red (CIR) and black and white aerial photography and field assessments are combined using a four-phase sampling for stratification approach. The statistical and operational aspects of a four-phase inventory are shown with special reference to the determination of optimal stratum boundaries. The method was applied in a pilot survey in Karnataka, India.