evidence: Venezuela and Guyana have been locked in a land dispute over the oil-rich Essequibo region which makes up about two-thirds of Guyana's territory, but has long been claimed by Caracas. [...] Venezuela's century-old claim on Essequibo has been revived since massive offshore oil deposits were discovered in the region and Guyana began handing out licenses to oil companies to operate there. [...] But Venezuela claims the Essequibo River to the region's east forms a natural border recognized as far back as 1777.