'O God' in the Bible

And Moses cried unto the LORD, saying, Heal her now, O God, I beseech thee.

And they fell upon their faces, and said, O God, the God of the spirits of all flesh, shall one man sin, and wilt thou be wroth with all the congregation?

And Balaam said unto God, Balak the son of Zippor, king of Moab, hath sent unto me, saying,