Oas, officially the Municipality of Oas (Central Bikol: Banwaan kan Oas; West Miraya Bikol: Banwaan nin Oas; ᜊᜈ᜔ᜏᜀᜈ᜔ ᜈᜒᜅ᜔ ᜂᜏᜐ᜔: Filipino: Bayan ng Oas), is a municipality in the province of Albay, Philippines. According to the 2024 census, it has a population of 64,890 people.

There are two stories that purport to tell the origin of the name of Oas:

a) There is a dam across the narrowest portion of a local river. This dam solely irrigates the vast fields of the place including those of the nearby town of Libon and results in a good harvest. People are wary of any cracks or leaks on the dam walls during months of heavy rains. A crier would shout nawaswas, giving the call to the people (in times of this kind of emergency) for immediate action in groups. From then on, the natives coined this name for the place and later shortened it to present form.

b) Early Spanish colonizers reaching this particular section of the Bicol Peninsula asked the name of the place from the about 600 natives living there, "Como se llama este sitio?" The natives mistakenly thought the question to be "Onan kading lugar kadi, maiwas?" ("What place is this, it's very big?") in their native language. In response, the natives answered, "Si, señores. Labi nikading iwas. Labi nikading iwas." ("Yes, sirs, this is grand and spacious".) From then on the early Spanish colonizers adopted in their official census the existence of "a rich fertile valley with verdant fields of grain" which is the little town of Oas in Bicol.

Oas was founded during the early Spanish colonization of the Bicol Peninsula. In 1605, Father Baltazar de los Reyes converted 12 leading natives of the area to Christianity in one day, forming the foundation of the community now known as Oas.

The town was one of the localities particularly harmed by the Dictatorship of Ferdinand Marcos; in the waning days of the dictatorship, Oas was hit by a series of political killings targeting those who dared to speak out against the abuses of the Military and against Ferdinand Marcos.

The most prominent of the victims was Clemente Ragragio, the municipal sanitation inspector of Ligao who was later also assigned to Oas. Known for his effectiveness, he had been awarded the 1983 Best Sanitary Inspector for Albay. However, this led the dictatorship's local administrators suspecting him of being a rebel sympathizer, because his close relationship with locals in far-flung barangays allowed him to move around fearlessly, and because he expressed disagreements with the dictatorship's governance. A killer shot him three times in front of his house in the early evening of August 21, 1985, and the government did not investigate his murder. He was later honored by having his name inscribed on the wall of remembrance at the Philippines' Bantayog ng mga Bayani (lit. Monument of Heroes), which honors the martyrs and heroes who fought to restore democracy in the wake of the Marcos dictatorship.

Oas has been in the news several times in recent years due to the achievements of its outstanding citizens, notably chess prodigy Bince Rafael Operiano who topped the under-10 age category at the 6th Eastern Asia Youth Chess Championship in Bangkok in 2022, and Miss Universe 2018 Catriona Gray whose maternal lineage has its roots in Oas.