Sibutu Passage is a deep channel some 18 miles (16 nmi; 29 km) wide that separates Borneo from the Sulu Archipelago. It has a deep sill allowing entry of deep water into the Sulu basin while connecting the Sulu Sea with the Sulawesi Sea that feeds from the Pacific Ocean by the Mindanao Current.

Although H. Otley Beyer argued in favor of a settlement of the Philippines across land bridges during the last ice age, modern bathymetric soundings have shown that the centers of the Sibutu Passage and the Mindoro Strait are both deep enough that they probably still existed at that time, although the Sulu and other Philippine Islands beyond were one connected island. If verified, therefore, the Callao Man would have needed to have crossed the open sea to reach the islands.

• Philippine Islands Sailing Directions, third edition of the bulletin prepared in the office of the United States Coast and Geodetic Survey at Manila by Harry L. Ford, nautical expert (Washington, DC: Bureau of Printing, 1906), p. 171
• Lambert Anthony B. Meñez, Cesar L. Villanoy and Laura T. David. "Movement of Water Across Passages Connecting Philippine Inland Sea Basins" (Marine Science Institute, University of the Philippines, November 6, 2006)
• Larena, Maximilian; Sanchez-Quinto, Federico; Sjödin, Per; McKenna, James; Ebeo, Carlo; Reyes, Rebecca; Casel, Ophelia; Huang, Jin-Yuan; Hagada, Kim Pullupul; Guilay, Dennis; Reyes, Jennelyn; Allian, Fatima Pir; Mori, Virgilio; Azarcon, Lahaina Sue; Manera, Alma; Terando, Celito; Jamero, Lucio; Sireg, Gauden; Manginsay-Tremedal, Renefe; Labos, Maria Shiela; Vilar, Richard Dian; Latiph, Acram; Saway, Rodelio Linsahay; Marte, Erwin; Magbanua, Pablito; Morales, Amor; Java, Ismael; Reveche, Rudy; Barrios, Becky; Burton, Erlinda; Salon, Jesus Christopher; Kels, Ma. Junaliah Tuazon; Albano, Adrian; Cruz-Angeles, Rose Beatrix; Molanida, Edison; Granehäll, Lena; Vicente, Mário; Edlund, Hanna; Loo, Jun-Hun; Trejaut, Jean; Ho, Simon Y. W.; Reid, Lawrence; Malmström, Helena; Schlebusch, Carina; Lambeck, Kurt; Endicott, Phillip; Jakobsson, Mattias (30 March 2021). "Multiple migrations to the Philippines during the last 50,000 years". Proceedings of the National Academy of Sciences. 118 (13): supplementary information. doi:10.1073/pnas.2026132118. hdl:1885/293505. ISSN 0027-8424. Retrieved 9 July 2024.

• Map of Sibutu Passage (channel), Philippines Encarta - MSN
• Malaysia Map - Malaysia Satellite Image - Geology.com