Private
The standard contract is ten years, darling. Your soul in exchange for his. He's brought back in one piece and you get ten years to spend topside with him. At the end of that period your soul is forfit to me. You spend eternity in the pit where you will probably become a demon.
Of course, I may find a reason to let you hold onto your soul for longer than ten years but that depends on how interesting you are.
Now, hearing all that, is your little Winchester worth it?