The peak fat oxidation rate (PFO) and the exercise intensity that elicits PFO (Fat(max)) are associated with endurance performance during exercise primarily involving lower body musculature, but it remains elusive whether these associations are present during predominant upper body exercise. The aim was to investigate the relationship between PFO and Fat(max)determined during a graded exercise test on a ski-ergometer using double-poling (GET-DP) and performance in the long-distance cross-country skiing race, Vasaloppet. Forty-three healthy men completed GET-DP and Vasaloppet and were divided into two subgroups: recreational (RS, n = 35) and elite (ES, n = 8) skiers. Additionally, RS completed a cycle-ergometer GET (GET-Cycling) to elucidate whether the potential relationships were specific to exercise modality. PFO (r(2) = .10,P = .044) and Fat(max)(r(2) = .26,P <.001) were correlated with performance; however,V & x2d9;O2peakwas the only independent predictor of performance (adj.R-2 = .36) across all participants. In ES, Fat(max)was the only variable associated with performance (r(2) = .54,P = .038). Within RS, DPV & x2d9;O2peak(r(2) = .11,P = .047) and ski-specific training background (r(2) = .30,P = .001) were associated with performance. Between the two GETs, Fat(max)(r(2) = .20,P = .006) but not PFO (r(2) = .07,P = .135) was correlated. Independent of exercise mode, neither PFO nor Fat(max)were associated with performance in RS (P > .05). These findings suggest that prolonged endurance performance is related to PFO and Fat(max)but foremost toV & x2d9;O2peakduring predominant upper body exercise. Interestingly, Fat(max)may be an important determinant of performance among ES. Among RS, DPV & x2d9;O2peak, and skiing experience appeared as performance predictors. Additionally, whole-body fat oxidation seemed specifically coupled to exercise modality.