The Cooper 12-Minute Run Test (CT12) is widely used to estimate cardiorespiratory fitness (CRF), yet its validity in collegiate team-sport athletes remains uncertain. This study aimed to compare the CT12-estimated VO2 max with laboratory-measured VO2 max and evaluate CT12's accuracy in classifying CRF levels. Seventy-three varsity athletes (38% women; age 21.6 ± 2.8 y; BMI 23.5 ± 3.3 kg/m2) completed CT12 on a 400-m track and a ramp-incremental treadmill test with breath-bybreath gas analysis, 2-7 days apart in randomized order. VO2 max was classified by age/sex criteria. Agreement statistics included paired tests, Pearson correlation, Bland-Altman bias, and 95% limits of agreement (LOA), 95% confidence intervals (CI), and diagnostic indices (sensitivity, specificity, positive/negative predictive value) for detecting good, excellent, and superior CRF. Field (soccer/rugby) and court (futsal/handball) subgroups were analyzed. CT12 on average underestimated VO2 max by 6.0 mL(kg.min)-1 (p