The production and trade of agricultural commodities, such as cocoa, have important impacts on farmer livelihoods and the environment, prompting a growing number of companies to adopt public commitments to address sustainability issues in their value chains. Though trading companies, who handle the procurement and export of these commodities, are key actors in corporate sustainability efforts, cross-country data on their identity, market share, and adoption of sustainability commitments is lacking. Here, we address this gap for the cocoa sector by compiling detailed shipping data from eight countries responsible for 80% of global cocoa exports, developing a typology of trader types, and assessing their adoption of sustainability commitments. We find that cocoa trading is a highly concentrated market: seven transnational companies handled 62% of the global cocoa trade, with even larger shares in individual cocoa producing countries. The remaining 38% of exports were handled by domestic trading companies and farmer cooperatives. Overall, the adoption of public sustainability commitments is low. We estimated that just over one quarter (26%) of cocoa is traded under some form of sustainability commitment, with gaps arising from their exclusion of indirect sourcing, low adoption rates by domestic traders, and commitment blind spots, notably on forest degradation and farmer incomes. Low rates of traceability and transparency pose a further barrier to the broadscale implementation and monitoring of these commitments: one-quarter of traders report being able to trace at least some of their cocoa back to farmer cooperatives and only half of them openly disclose the identity of their suppliers. We discuss the opportunities and limitations of voluntary sustainability commitments in a highly concentrated market and argue that, to realize visions of sustainable trade, the gaps in commitment coverage must be closed by extending current efforts to smaller traders and indirect suppliers. However, companies must support, coordinate and align with government efforts so that voluntary initiatives are ultimately rendered more transparent and accountable.