Of the fatalities, four were children aged three months to 10, police said.
Superintendent Enrique Ramos, Oas police chief, said only five of the 13 fatalities have so far been identified by their relatives.
The five were Maria Victoria Alverga, her daughters Ma. Vanessa, 10, and Rubic, 3; Edilyn Mamangon and Jannel Abache, 7, all from the third district of Albay.
Twelve of the 13 fatalities, who were all passengers of the jeepney, died on the spot, while the 13th, a still unidentified woman, died while she was being treated at the Bicol Regional Training and Teaching Hospital here.
The injured were rushed to the Josefina Belmonte Duran Memorial Hospital in Ligao City and the Roa Hospital in Oas town.
Investigation showed that the Uy Transit bus was trying to overtake another vehicle when it smashed into the passenger jeepney which was on the opposite lane. The jeep, which was a total wreck, then hit a van behind it.
The bus driver, a certain Jose Binaday, was arrested. He is now detained in the Oas jail.
Doctors said a number of those injured were still in critical condition.