Background/Objective Measures of oxygen uptake efficiency (OUE) have been used to evaluate cardiorespiratory fitness (CRF) in adolescents unable to perform maximal exercise. The oxygen uptake efficiency slope (OUES) and oxygen uptake efficiency plateau (OUEP) have been proposed as surrogates for maximal oxygen consumption (V̇O 2max ). We assessed the validity of the OUES and OUEP as predictors of V̇O 2max in healthy male adolescents. Methods Sixty-three healthy male adolescents aged 15.40 ± 0.34 years underwent an incremental treadmill test to determine V̇O 2max , OUES and OUEP. OUE throughout the test was assessed by dividing each V̇O 2 value by the corresponding minute ventilation (V̇ E ) value. OUEP was determined as the 90 sec average highest consecutive values for OUE. OUES was determined using data up to the ventilatory threshold (VT) by calculating the slope of the linear relation between V̇O 2 and the logarithm of V̇ E . Results Limits of agreement for V̇O 2max predicted by OUES (± 13.3 mL.kg -1 .min -1 ) and OUEP (± 16.7 mL.kg -1 .min -1 ) relative to V̇O 2max were wide and a magnitude bias was found for OUES and OUEP as predictors of V̇O 2max (p<0.001). Conclusion The OUES and OUEP do not accurately predict V̇O 2max in male adolescents and should not replace V̇O 2max when assessing CRF in this population.