Reviews in outline the theoretical and practical aspects of an acoustical method of detecting oil trapped under sea ice. Following discussion of the theoretical problems, information relating to acoustical mode conversion in the ultrasound reflected from the lower side of the ice is presented. An experiment in a large salt water tank, with about 80 cm of ice, is described and the results are related to theory which is presented. A commentary on the lessons learned from this experiment is given. An outline of the design for a prototype field apparatus is presented.