For the sake of God. so 'For God's sake' is the correct form.
If your British. If you're American, it's "For God's Sake". LOL Danged Brits down know their quotation marks from an apostrophe in the ground.
I'm not British, I do know however it is 'If you're British'. The single quote and the apostrophe are, as you know, different. They may look the same, but they are not. The single quote is used correctly, the double quote, or citation mark, is used for, as the name implies, citations.
For God's Sake. Singular possessive
If you refer to multiple Gods....then Gods' would be correct.
oh, for God's sake! can't you tell?
hang on ... I'll ask God for you
Either is acceptable.
Sake = For the purpose of; in the interest of; in order to achieve or preserve.<br />
Thereby for the sake of God, of which there is singularly only one, "for God's sake" would be grammatically acceptable, but " for the sake of God", would be grammatically preferable.
God's sake or Gods' sake if you mean several gods
It is genitive, so it should be 'God's sake'...But I'm a stranger and we tend to be correct as much as we can, cause we don't know better.