The ocean economy is growing as commercial use of the ocean accelerates, while progress toward achieving international goals for ocean conservation and sustainability is lagging. In this context, the private sector is increasingly recognized as having the capacity to hamper efforts to achieve aspirations of sustainable ocean-based development or alternatively to bend current trajectories of ocean use by taking on the mantle of corporate biosphere stewardship. Here, we identify levels of industry concentration to assess where this capacity rests. We show that the 10 largest companies in eight core ocean economy industries generate, on average, 45% of each industry's total revenues. Aggregating across all eight industries, the 100 largest corporations (the Ocean 100) account for 60% of total revenues. This level of concentration in the ocean economy presents both risks and opportunities for ensuring sustainability and equity of global ocean use.