Many large-scale transportation systems rely on decision-makers who independently allocate resources across space and time. While decentralization fosters competition, it can also generate substantial operational inefficiencies. We study this trade-off in the global oil tanker market, where approximately half of all miles are traveled without cargo (ballasting). Although some empty repositioning is unavoidable due to geographic imbalances in oil trade, the extent to which market structure contributes to this inefficiency has not been quantified. Methodology/results: We develop a framework that decomposes observed empty miles into shares attributable to trade imbalances, demand uncertainty, and market fragmentation. Using granular commercial data, we show that fragmented ownership accounts for 7–16% of total empty miles, a “fragmentation tax” roughly twice the share attributable to demand uncertainty. These inefficiencies arise because independent owners optimize over limited fleet footprints and cannot internalize cross-fleet balancing externalities. Our decomposition also isolates the share of emissions induced by ownership fragmentation from that caused by structural trade patterns, identifying the portion of carbon emissions that is operationally addressable. Focusing on the growing industry trend of shipping pools, we show that even modest consolidation captures most of the gains achievable under full centralization, while preserving competitive market structure. Managerial implications: Our findings provide quantitative evidence that modest consolidation in large-scale spatial allocation systems can deliver substantial efficiency gains without requiring high market concentration, establishing operational coordination as a practical complement to technological and regulatory approaches that currently dominate the decarbonization agenda.