I also posted this the boats/motors forum.

I need to verify my outboard's hp for a tournament, and need to find the serial number on my motor. Can anyone tell me where it is at? It's a 2003 Mercury 150hp.

Thanks.

Stand behing the motor and look around the housing on the starboard side. You should see a little plate with the number on it. Or you could just look at your title.

On the shaft housing, starboard side.