Petrolia is a borough in Butler County, Pennsylvania, United States.

[3] Petrolia is located in eastern Butler County at 41°1′5″N 79°43′6″W / 41.01806°N 79.71833°W / 41.01806; -79.71833 (41.017964, −79.718204),[4] in the valley of the South Branch of Bear Creek, a tributary of the Allegheny River.

According to the United States Census Bureau, Petrolia has a total area of 0.39 square miles (1.0 km2), all land.

20.2% of all households were made up of individuals, and 6.7% had someone living alone who was 65 years of age or older.

About 8.5% of families and 14.5% of the population were below the poverty line, including 23.1% of those under the age of eighteen and none of those sixty five or over.