This is a double-blind (neither the patient nor the study doctor knows the name of the assigned study drug during the study), randomized (study drug selected by chance like flipping a coin), active-comparator (patient will get active drug and there is no inactive drug), outpatient study to evaluate efficacy and how well a patient tolerates multiple doses of tapentadol immediate release (IR) versus oxycodone IR for short-term moderate to severe post-operative pain after arthroscopic (a surgical technique whereby a doctor inserts a tube-like instrument into a joint to visually inspect and repair tissues) shoulder surgery. About 370 patients will be enrolled to either receive tapentadol IR or oxycodone IR until approximately 150 patients in each treatment group are enrolled. After obtaining informed consent, patients will have screening visit procedures to determine study eligibility. Visit 1 (screening) may begin up to 21 days prior to surgery. Pre-operative assessments (e.g., physical examinations, clinical laboratory assessments) will be conducted as part of routine procedures. Patients will have a urine drug test and women who are able to have children will have a urine pregnancy test performed as part of screening prior to the study. Height and weight will be taken and a sleep questionnaire will also be completed at screening. Study staff will conduct pre-operative teaching regarding post-operative pain including: the pain intensity assessment for the study (11-point numeric rating scale where 0=no pain and 10=pain as bad as you can imagine); descriptions of mild, moderate and severe pain; instructions for dosing with study medication; and completing the study diary. Eligible patients will be post-operative men and women who have undergone elective outpatient arthroscopic shoulder surgery. Patients must have received a regional interscalene (within the scalene muscles) nerve block as the primary anesthetic (numbing medication) during the procedure and do not require intravenous (through a vein) patient-controlled analgesia post-operatively. Patients who are expected to have moderate to severe acute post-operative pain from shoulder surgery and who are appropriate candidates for outpatient pain management with an oral opioid (narcotic) pain medication will be eligible. In addition, appropriate patients are expected to require oral opioid pain medication post-operatively. Patients who continue to meet all study criteria post-operatively will be assigned to a study drug group prior to PACU discharge (PACU is considered Visit 2) and will be sent home with study medication. All patients will be prescribed a standard regimen of cold pack application to the surgical shoulder. Patients will be instructed to take the first dose of study medication as their first oral pain medication when they have at least "moderate" pain (prior to discharge or at home). Patients will be reminded about instructions on post-operative pain that were discussed during the pre-operative screening visit. Patients will also be instructed to complete a diary assessment of their current pain intensity before taking the first dose of study medication. Day 1 will be the calendar day when the patient takes the first dose of study medication. Starting on Day 1, patients will be instructed to complete assessments in paper diaries each morning and evening related to pain intensity, pain relief, and occurrences of vomiting. All patients will be contacted by telephone by a member of the study staff on the day following surgery. The staff will verify that the first dose of study medication was taken and the baseline pain intensity assessment was recorded. All patients will receive a second telephone call from the study staff on Day 3. During this telephone call, site personnel will inquire about the patient's overall status and will reinforce diary compliance. If the study staff determines it is necessary, the patient will be required to return to the study site for an unscheduled visit. Patients may take up to 2 pills (any form) of acetaminophen for pain other than post-operative shoulder pain (e.g., headache, back pain) once per day only for up to a total of 2 days during the study. Patients who take up to 325 mg/day aspirin as prevention for a heart condition will be permitted to enter the study and continue on study medication provided they are on a stable dose for at least 1 month prior to study entry and plan to continue the same dose during the study. Patients who complete the study will return to the study site for a final visit (Visit 3) on Day 7. Patients who discontinue early for any reason (i.e., lack of efficacy, adverse events, patient's choice) should contact the study staff before taking supplemental pain medication and schedule his/her final visit. Patients will complete a final assessment of pain intensity and pain relief. In addition, all patients will complete a sleep questionnaire, a Patient Global Impression of Change and an assessment of satisfaction with treatment. The study doctor will complete a Clinician Global Impression of Change and will record any medical resource utilization noted in the office charts (e.g., unplanned calls from the subject, unscheduled office visits, emergency room visits). Vital signs will be obtained and study medication will be collected and counted. Patients will have adverse events assessed and any changes in concomitant medications (other medications taken at the same time as the study medication) recorded. All patients will have post-study medication prescribed at the study doctor's discretion. A patient may elect to take supplemental pain medication to treat their post-operative shoulder pain at any time during the study; however, patients who take supplemental pain medication will be considered discontinued from the study. Patients will be assigned by chance equally (1:1) in a blinded (neither the patient or study doctor knows) fashion to get tapentadol immediate release (IR) 50 or 100 mg vs oxycodone IR 5 or 10 mg, every 4-6 hours as needed. Treatment is up to 7 days starting on Day 1 with one capsule of study medication. A "re-dose" is permitted and may be administered as soon as one hour after the first dose only. For subsequent doses, patients may take one or two capsules every 4 to 6 hours as needed.