This paper reinterprets the Ottoman public debt crises of the late nineteenth century as part of a global history of modern accounting and statistics. Scholars have devoted much attention to public debt in the late Ottoman Empire’s economic and political transformations. From 1881 until World War I, an increasing number of the Empire’s most productive sectors fell under the aegis of the Ottoman Public Debt Administration, which introduced new techniques in agriculture, mineral extraction, and transportation. Meanwhile, in Cairo, the Caisse de la Dette helped pave the way for indirect colonial rule under the British Occupation. These developments are centerpieces of a rich literature in late Ottoman economic history, political and diplomatic history, and political economy. But public debt can also be understood, using methods from science studies, as a problem of knowledge. In addition to posing economic, political, and legal challenges to the late Ottoman state, the negotiation and management of public debt also posed new problems of quantification for Ottoman bureaucrats, as well as European investors, financiers, and statesmen. In fact, what economic and political history have treated as fundamental facts of the Ottoman debt—how much of it there was, and to whom it was owed—were questions that eluded easy consensus in the late nineteenth century: a period, as historians of science have shown, when the growth of bureaucratic nation-states and empires drove the emergence of new forms of statistical reasoning. In this light, it becomes necessary to ask how particular social groups, from the OPDA in Istanbul to the Council of Foreign Bondholders in London, came to agree on the premises and techniques that would govern the quantification of Ottoman debt. In pursuing an answer to this question, this paper demonstrates how public debt linked late Ottomans with the newly independent states of Central and South America, the other major region in which European bankers facilitated ruinous loans in the late nineteenth century. Focusing on the network of the English banker Haim Guedalla, and drawing on the records of the Council of Foreign Bondholders, the paper argues that Ottoman financial crises were shaped by, and contributed to, the emergence of globalized techniques for managing public debt.