At least 10 people, including six teenagers, were killed and 16 others injured when a school bus collided with a tanker truck in Brazil's Sao Paulo state, the highway patrol said.The accident occurred Monday night on the highway near Ibitinga city, about 300 km from Sao Paulo city.Six students between the ages of 15 and 17, three teachers and the principal of the Dom Gastão Liberal Pinto public school in the city of Borborema died in the accident.The group had been on a field trip to Sao Paulo, the highway patrol said.The bus, carrying 40 people, collided with a tanker truck hauling vegetable oil. The oil spilled on the highway and started a fire.The school group visited the Latin America Memorial in Sao Paulo, the Borborema city government said.