Firefighters Tuesday extinguished a fire at Venezuela's largest oil refinery, three days after it was ignited by an explosion that killed at least 40 people, company sources said. "We can say the fire is completely out," said a source at state-owned Petroleos de Venezuela, speaking on condition of anonymity. The fire had spread to a third storage tank at the Amuay refinery in Punto Fijo, sending up towering flames before firefighters succeeded in extinguishing it early Tuesday, according to the company sources. An AFP reporter at the scene said only smoke could be seen rising from the third storage tank. The fire at the other two tanks were put out earlier. The fire began with an explosion that tore through the refinery early Saturday, killing at least 40 people in the deadliest accident ever for the state oil giant. Most of the dead were from a national guard unit assigned to guard the facility, and members of their family. The refinery is located in a residential and commercial complex where workers live with their relatives and poor families who settled in surrounding neighborhoods. Authorities said 209 homes and 11 businesses had been affected. Oil Minister Rafael Ramirez, who is also the president of PDVSA, said Monday that the fire would not affect oil derivative exports or domestic supplies in Venezuela, an OPEC member and Latin America's biggest petroleum producer. He said the country's other five domestic refineries could produce 735,000 barrels of fuel per day to take up some of the slack, while insisting that "all our export capabilities are intact." President Hugo Chavez, who is recovering from cancer and running for reelection October 7, toured the scene dressed in mourner's black and hugged weeping family members. The elected president since 1999, he has shrugged off suggestions infrastructure could have weakened under his long watch. Ramirez has also said the Paraguana facility -- which includes the Amuay and Cardon refineries -- will be able to operate at full capacity within two days after the fire is extinguished. But Jose Bodas, general secretary of the United Federation of Oil Industry Workers, questioned that assessment on Monday. "It appears to us that it is too early to talk about resuming production without knowing the exact cause of the explosion," Bodas told AFP. The Amuay refinery was capable of producing 645,000 barrels per day before the incident, while the Cardon put out 310,000 bpd, according to official figures. The two facilities account for 66 percent of local demand. Venezuela's heavily-subsidized gasoline is among the cheapest in the world. The Latin American nation produces about three million barrels of oil per day, according to state figures, while the Organization of the Petroleum Exporting Countries (OPEC) puts the number at 2.3 million barrels per day. OPEC certified in 2011 that Venezuela had the largest oil reserves in the world at 296.5 billion barrels, surpassing Saudi Arabia, the country with the biggest refining capacity. In March, Venezuela said the reserves were even higher, at 297.57 billion.