Tapentadol (CG5503) is a centrally active pain-relieving drug being investigated for the treatment of acute and chronic pain. This study is a randomized (patients are assigned different treatments based on chance in a ratio of 4 patients on tapentadol (CG5503) PR to every 1 patient on oxycodone CR), open-label (both the Investigator and the patient know what medication is allocated), active-controlled, parallel-group, multicenter study. It is designed to investigate the long-term safety (side effects during up to one year of administration) and effectiveness (level of pain control) of tapentadol (CG5503) PR compared to oxycodone CR (an opioid commonly used for relief of moderate to severe pain) taken orally. The study consisted of a screening period (up to 14 days), a washout period (3 to 7 days), and an active treatment phase with titration and maintenance (total duration of 52 weeks). The doses of both of these medications will be adjusted to give the best therapeutic benefit for the patient. A total of 1123 patients will be screened. Safety evaluations include monitoring of adverse events, physical examinations, and clinical laboratory tests. Assessments of pain relief include the pain intensity numerical rating scale, and patient global impression of change scale (PGIC). Venous blood samples will be collected for the determination of serum concentrations of tapentadol (CG5503) and oxycodone. Tapentadol (CG5503) PR is also referred to as Tapentadol (CG5503) Extended Release (ER). Starting oral dose is randomly assigned to tapentadol (CG5503) PR 50 mg or oxycodone CR 10 mg twice daily (BID) x 3 days; then increase to tapentadol (CG5503)100 mg BID, oxycodone CR 20 mg BID x 4 days; during the maintenance phase upward titration may occur at a minimum of 3 day intervals in increments of tapentadol (CG5503) PR 50 mg BID or oxycodone CR 10 mg BID. The maximum doses are tapentadol (CG5503) PR 250 mg BID or oxycodone CR 50 mg BID.