If an oceanic plate is subducting on its eastern side, the most likely boundary type on the western side of the plate would be a divergent boundary. This is because as the plate subducts and sinks beneath another plate, it is being destroyed, and new magma is being produced at the divergent boundary to replace it. The new magma then rises to the surface, creating new oceanic crust. Therefore, the western side of the plate would be moving away from the eastern side, creating a divergent boundary.