Which Titan god of the sea was father to the Oceanids?

The Titan god of the sea who fathered the Oceanids was Oceanus.

Oceanus was one of the twelve original Titans, born to Uranus, the sky, and Gaia, the earth. Unlike Poseidon, who later ruled the sea from Mount Olympus, Oceanus represented the enormous world-encircling river that ancient Greek cosmology imagined flowing around the inhabited world.

Oceanus married his sister, the Titaness Tethys. Together they were said to have produced the Oceanids, water nymphs associated with springs, streams, and other bodies of water. Hesiod gives their number as three thousand, a figure indicating abundance rather than a census of individually known daughters.

The Oceanids include important mythological figures such as Metis, Zeus’s first wife; Styx, a divine river associated with oaths; Doris, mother of the Nereids; and Clymene, traditionally linked with the family of Iapetus. Oceanus is therefore not the same figure as Poseidon or Nereus: all are connected with water, but they occupy different places in Greek mythological genealogy.