The purpose of this study was to compare running economy across three submaximal speeds expressed as both oxygen cost and the energy required to cover a given distance in a group of trained male distance runners. It was hypothesized that expressing running economy in terms of caloric unit cost would be more sensitive to changes in speed than oxygen cost by accounting for differences associated with substrate utilization. 16 highly-trained male distance runners ( 66.5±5.6 ml^.kg^-1.min^-1, body mass 67.9±7.3 kg, height 177.6±7.0 cm, age 24.6±5.0 years) ran on a motorized treadmill for 5 minutes at zero slope and speeds corresponding to 75, 85 and 95 % of speed at lactate threshold. Oxygen uptake was measured via open-circuit calorimetry. Average oxygen cost was 221±19, 217±15 and 221±13 ml^.kg^-1.km-^-1, respectively. Caloric unit cost was 1.05±0.09, 1.07±0.08 and 1.11±0.07 kcal^.kg^-1.km^-1 at the three trial speeds, respectively. There was no difference in oxygen cost with respect to speed (p=0.657); however, caloric unit cost significantly increased with speed (p<0.001). It was concluded that expressing running economy in terms of caloric unit cost was more sensitive to changes in speed and is a more valuable expression of running economy than is oxygen uptake.