The placement of a catheter in the thoracic epidural space remains a challenge for the anesthesiologist. Suboptimal placement of the catheter within the epidural space can result in inadequate pain relief. The distance at which the catheter must be advanced in the thoracic epidural space remains unknown. Insertion distance could influence the initial quality and distribution of sensory blockade, its duration, or both. Therefore, this study is designed to compare three catheter insertion distances, in order to help determine which is best for pain relief after a thoracotomy.