Ogori masu. ／ Watashi no ogori desu.

                     (translation: It's on me. ／　It's my treat.)

Ex.

      1. A : Everything sounds so delicious on this menu list. I don't know

          which to try..

          B : Konya wa watashi no ogori desu ( It's my treat tonight.)

          So you get whatever you want,ok?  

　　　2.  A: Here is your Sake.

           B : Thanks, how much was it? I pay you back.

           A : Don't worry. Ogori masu ( It's on me.)