Back then, geologists relied on mapping and flat-tableting exposed rock formations, but most of Abu Dhabi's hinterland was covered in sand. Due to the apparent delay in excavations, the PDTC acquired a 75-year concession for the entire emirate. Finally, in 1951, the PDTC began drilling at Ras Sadr and Jebel Ali with holes up to 13,000 feet deep. Unfortunately both locations revealed a dry well. After this setback the PDTC's intention was to go to the western border of Abu Dhabi where oil was suspected to be present. Saudi Arabia on the opposite border disputed this sovereignty interest because the drilling area was within the 20-mile diameter of the Buraimi Oasis, a place of historical significance. Subsequently the dispute, now known as the Buraimi dispute, was resolved in Saudi Arabia's favor under the Jeddah Treaty and closed parts of Abu Dhabi to oil.