Drain oranges and pineapple, reserving juices. Set oranges and pineapple aside. Add water to juices to measure 2 cups. Place in a saucepan and bring to a boil; pour over gelatin in a large bowl. Stir until gelatin is dissolved. Stir in sherbet until smooth.
Chill until partially set (watch carefully). Fold in oranges, pineapple and bananas. Pour into an oiled 6-cup mold. Chill until firm.