Oil exploration in the Belait District started as early as 1911, and a modest strike at Labi in 1914 was enough to convince prospectors that the geology held promise. A 97-kilometer road was cut from Kuala Belait to Brunei Town that same year, the first real infrastructure linking the two settlements. Oil companies concentrated their operations around the Belait River, and by 1927 a thriving village had formed at its mouth, serving as the port where drilling machinery arrived by sea. The British Malayan Petroleum Company -- later Brunei Shell Petroleum -- made Kuala Belait its headquarters in 1929, the same year that Seria Well No. 1 struck oil just down the coast. That discovery changed everything. Kuala Belait became the administrative seat of Belait District, a Sanitary Board was established to govern the growing town, and an Assistant British Resident was posted there to oversee London's petroleum interests.

The 1930s arrived with the force of a boom. In 1930, the BMPC strung a telephone line along the Belait coastline, connecting Seria and Rasau to headquarters. Brunei's first English-language school opened in Kuala Belait in 1931, and the town boasted the best hospital in the country. The population swelled from 1,193 in 1931 to 3,000 by 1935, then to 5,000 by 1938. The BMPC was the district's largest employer, with 1,185 of 2,265 workers on its payroll. Pipelines and roads linking Kuala Belait to Miri in Sarawak were completed by 1939. Not everything worked. A telephone line to Tutong was dismantled in 1934 after failing to meet expectations -- a reminder that even oil money could not guarantee every venture's success. But the trajectory was unmistakable. A village at a river mouth had become the engine room of a small nation's economy.

On December 16, 1941, roughly 10,000 soldiers of the Japanese Kawaguchi Detachment launched an amphibious assault on the Belait coast. Kuala Belait fell quickly. The occupation that followed brought atrocity. Japanese forces massacred and executed Indian prisoners of war from the 2/15th Punjab Regiment. Another 55 Indian prisoners died of starvation in the town's POW camp. The town itself was heavily bombed, leaving much of it in ruins. Liberation came on June 24, 1945, when the Australian 9th Division recaptured the port as part of Operation Oboe Six. Reconstruction plans were not approved until 1949, and the process of rebuilding transformed Kuala Belait's physical character -- reinforced concrete shophouses, government offices, godowns, and a new wharf replaced what the war had destroyed. By the early 1950s, the town had been modernized almost beyond recognition.

The postwar years brought a different kind of tension. In 1950, the Brunei government grew concerned about the potential spread of Chinese Communist ideology among Kuala Belait's urban working class -- the town had a sizable Chinese population, many of them oil industry workers. The police headquarters was relocated from Brunei Town to Kuala Belait, and both a Criminal Investigation Department and a Special Branch were established to monitor the situation. The anxiety was not unique to Brunei; across Southeast Asia, colonial and newly independent governments were grappling with communist movements. But the decision to concentrate security apparatus in an oil town, rather than the capital, says something about where the government believed its vulnerabilities lay. Meanwhile, the oil wealth continued to accumulate. Sultan Omar Ali Saifuddien III initiated plans in 1952 to build a country palace in Kuala Belait, a mark of the town's rising status.

Today Kuala Belait's population hovers around 4,500 in the town proper, modest for a place of such economic significance. The Belait District Museum preserves the region's history. Silver Jubilee Park commemorates Sultan Hassanal Bolkiah's twenty-five years on the throne. The Mohammad Jamalul Alam Mosque anchors the town center. Water taxis still depart from the public wharf near the market, carrying passengers upriver toward Kuala Balai, the traditional heartland of the indigenous Belait people. The Kuala Belait Boat Club organizes sailing trips to the open sea. For all the oil that reshaped this coast, the town remains defined by its river -- by the silting mouth that still needs breakwaters, by the tidal rhythms that governed life here long before anyone drilled a well.