Purpose: Examine differences in measures of cardio-respiratory fitness and determinants of running economy with respect to maturity status, in a group of highly trained youth soccer players. Methods: Twenty-one highly trained youth soccer players participated. On separate visits, players’ peak oxygen uptake, running economy, at three different speeds (8km•h-1, 80%GET and 95%GET), and pulmonary oxygen uptake kinetics (VO2 kinetics) were determined. Players also performed a Yo-Yo Intermittent Recovery test level 1 (Yo-Yo IR1). Players were categorised as either ‘pre-PHV’ or ‘mid-PHV’ using the measure of maturity offset. Independent t-tests and Cohen’s d effect sizes were then used to assess differences between groups. Results: The mid-PHV group were significantly taller, heavier and advanced in maturity status. Absolute measures of VO2peak were greater in the mid-PHV group, however, when expressed relative to body mass, FFM and theoretically derived exponents, VO2peak values were similar between groups. Pre-PHV group presented a significantly reduced VO2 response, during relative submaximal running speeds, when theoretically derived exponents were used, or expressed as %VO2peak. VO2 kinetics (tau) were faster during a low (standing) to moderate (95% GET) transition in the pre-PHV group. Yo-Yo IR1 performance was similar between groups. Conclusion: While measures of VO2peak and Yo-Yo IR1 performance are shown to be similar between groups, those classed as Pre-PHV display a superior running economy at relative submaximal running speeds and faster taus during a low-moderate exercise transition, than their more mature counterparts.