Maximal oxygen uptake (VO2max) is regarded as the gold standard for assessing aerobic fitness. In 1923, Hill et al. proposed that VO2max represents the maximal ability of the body to take in and consume O2 during strenuous exercise. Recently, however, controversy has arisen over the issue of whether a leveling off, or "plateau" in VO2 is necessary to verify attainment of VO2max. Purpose: To compare two different VO2max protocols and determine if both protocols show direct evidence of an upper limit on VO2. Methods: Nine runners (18-35 years old) completed a continuous graded exercise test (CGXT), followed by a discontinuous graded exercise test (DGXT). The CGXT consisted of gradually increasing treadmill running speed to the point of volitional exhaustion; the highest speed attained was labeled the peak treadmill speed. Over the next several days, participants ran at 80%, 90%, 100%, 105%, and 110% of peak treadmill speed for 10 minutes, or until volitional exhaustion was reached. Results: All participants (n=9) achieved a "VO2 ceiling" (or upper limit) on the DGXT, while only 44% (n=4) achieved a "VO2 plateau" on the CGXT. There was no significant difference between the VO2max obtained from a CGXT (57.4 ± 2.6 mL*kg-1min-1) and DGXT (60.0 ± 3.1 mL*kg-1min-1). There was no difference between oxygen uptake measured at 90%, 100%, 105%, and 110% of PTV (p>0.05). However, the highest VO2 recorded at 80% PTV was significantly lower than that recorded at all other velocities (p<0.05). Conclusion: The VO2 ceiling effect on a DGXT is inherently different than the VO2 plateau effect on a CGXT. In this study, a ceiling was always seen on the DGXT, but a plateau was not always seen on the CGXT.