'O God' in the Bible

And Moses cried to Jehovah, saying, O God, heal her, I beseech thee!

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

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