Situated roughly between 16° and 20° S and 58° and 50° W, the limits of Pantanal are not unanimously accepted. Descending from Serra das Araras, near the border of Mato Grosso with Bolivia, the Paraguay River flows into an immense alluvial plain that in Brazil alone measures 770km from north to south and has an area of approximately 139,000 km2 (Ferreira et al. 1993) The western end of this plain is traversed by the Paraguay River. It extends into neighboring countries (Bolivia, Paraguay, and to a lesser degree, Argentina) always along the margin of the river bed, in a total of about 230.000km2.

Pantanal's alluvial plain varies between 80-150m in altitude, with a north-south slope of only 2cm/km (Dubs,1992). On the Brazilian side (East, North and West), it is surrounded by the crystalline plateau, approximately 600-700m in altitude, which is covered with cerrado (scrubland) vegetation. To the South, there is the Paraguay depression, a rolling plain with an extensive hydrographic network, formed by countless tributaries of the gigantic Paraguay River. These alluvial plains are very thick; drilling in this area has reached 83m without hitting bedrock.