The oceans drain approximately 83% of the land in the world. The other 17% – an area larger than the basin of the Arctic Ocean – drains to internal endorheic basins.
Note that there are substantial areas of the world that do not "drain" in the commonly understood sense. In Arctic deserts much of the snowfall sublimates directly into the air and does not melt into flowing water, while in equatorial deserts precipitation may evaporate before joining any substantial water course. However, these areas can still be included in topographically defined basins if one considers the hypothetical flow of water (or ice), and thus nutrients or pollutants, over the surface of the ground (or ice sheet); this is the approach taken here. For example, the Antarctic ice sheet can be divided into basins, and most of Libya is included the Mediterranean Sea basin even though almost no water from the interior actually reaches the sea.