" I owe you one " is said when someone did you a great favour, and you kinda want to let that person know that you would do something back for him/her next time when he/she needs a favour :) Whereas " thank you " is merely just to express simple thanks for almost anything just for that moment, and that's it. :) Hope this helps. :)

i own you one = that someone did something to you and you want to return the favour Example : Thanks for helping me out, Bob. I owe you one! One of my friends helped me out . I am really grateful to him . ...................................... thank you : to thank orally someone without giving or doing something in return to him

i think maybe i owe you one means "i will pay back or help you when sb. need"

If I tell you, you'll owe me one. I don't want a thank you. I want all your yen. :P

If you say "I Owe you one" it means that you want to return the favor :)