To evaluate the efficacy and safety of tapentadol extended release (ER) for the management of moderate to severe chronic low back pain. Patients (N = 981) were randomized 1:1:1 to receive tapentadol ER 100 - 250 mg b.i.d., oxycodone HCl controlled release (CR) 20 - 50 mg b.i.d., or placebo over 15 weeks (3-week titration period, 12-week maintenance period). Efficacy was assessed as change from baseline in average pain intensity (11-point NRS) at week 12 of the maintenance period and throughout the maintenance period; last observation carried forward was used to impute missing pain scores. Adverse events (AEs) were monitored throughout the study. Tapentadol ER significantly reduced average pain intensity versus placebo at week 12 (least squares mean difference vs placebo [95% confidence interval], -0.8 [-1.22, -0.47]; p < 0.001) and throughout the maintenance period (-0.7 [-1.06,-0.35]; p < 0.001). Oxycodone CR significantly reduced average pain intensity versus placebo at week 12 (-0.9 [-1.24,-0.49]; p < 0.001) and throughout the maintenance period (-0.8 [-1.16,-0.46]; p < 0.001). Tapentadol ER was associated with a lower incidence of treatment-emergent AEs (TEAEs) than oxycodone CR. Gastrointestinal TEAEs, including constipation, nausea, and vomiting, were among the most commonly reported TEAEs (placebo, 26.3%; tapentadol ER, 43.7%; oxycodone CR, 61.9%). The odds of experiencing constipation or the composite of nausea and/or vomiting were significantly lower with tapentadol ER than with oxycodone CR (both p < 0.001). Tapentadol ER (100 - 250 mg b.i.d.) effectively relieved moderate to severe chronic low back pain over 15 weeks and had better gastrointestinal tolerability than oxycodone HCl CR (20 - 50 mg b.i.d.).