We are developing Spilled Oil Tracking Autonomous Buoy System (SOTABS), which is composed of a land base and several spilled oil tracking autonomous buoys (SOTAB), to detect and track spilled oil autonomously, sending real time data around them to the land base. This paper firstly deals with steady sailing performance of SOTAB-II with a sailboat shape for tracking spilled oil on the sea surface by controlling the rudder angle, and the area and direction of the sail, and then sea trials using a model of SOTAB-II with a cylindrical buoy shape to obtain its fundamental characteristics on motion. ©2010 IEEE.