The Tagus Basin is the drainage basin of the Tagus River, which flows through the west of the Iberian Peninsula and empties into Lisbon. It covers an area of 78,467 km2, which is distributed 66% (55,645 km2) on Spanish territory and 34% on Portuguese land (22,822 km2). It is the third largest basin in the Iberian Peninsula, after the , with 98,258 km2, and the Ebro Basin, with 82,587 km2.