This study assessed the influence of speed on the metabolic and the mechanical cost to run a given distance. Trained male runners (n=12) performed 2 treadmill run trials of 8 min duration at each of 6 speeds (range 2.33 to 4.0 m.s-1). Oxygen uptake values were normalized for running speed providing a metabolic task cost variable (MBTC, ml.kg-1.m-1). Mechanical power was calculated from digitized video records using three different algorithms. Values were normalized for running speed giving mechanical task cost variables (MTC, J.kg-1.m-1). Repeated measures ANOVA revealed no differences between the trials for both MBTC and MTC (p = 0.99). MTC from the three algorithms were significantly different from each other (p < 0.001). Regression analyses revealed that MTC decreased as speed increased (p<0.001). No change in MBTC was found across speeds (p=0.25). This study suggests that metabolically it is no more costly to run a kilometer at 4 m.s-1 than at 2.33m.s-1. Mechanically, however, it is more economical to run at 4 m.s-1 than at 2.33 m.s-1.