Abstract: A drill stem stabilizer used in a decoking apparatus that includes a drill stem and a drilling structure on which the drill stem is supported for vertical movement above and within a coke drum. The stabilizer includes a bearing and a support member. The bearing is adapted to guide the longitudinal movement of the drill stem. The support member extends laterally from the bearing and attaches to the drilling structure, and maintains the bearing in a position to guide the drill stem as it is moved into or out of the coke drum. In one embodiment, the drilling structure includes a pair of substantially vertical guide rails, and the support member attaches to the guide rails.