Mare Nectaris (the "sea of nectar") is a lunar mare located within the Nectaris basin on the lunar nearside. The basin material is of the Nectarian and Lower Imbrian epochs, with the mare material of the Upper Imbrian epoch. The crater Theophilus on the northeastern side of the mare is of the Eratosthenian epoch. Thus, the crater is younger than the mare to its southeast. Montes Pyrenaeus borders the mare to the west.

The mare material is approximately 1000m in depth. Enough subsistence has occurred to open a few arcuates grabens on the western margin of the mare. The large crater near the south center of the mare is Rosse.