The fire was reported shortly before 9:30 p.m. in an apartment building in the 1600 block of Detroit Avenue, Contra Costa County Fire Protection District spokeswoman Emily Hopkins said.
"It was a cooking fire, started by a man who was heating oil on his stove," she said. "He got burned trying to move the pan."
Medics treated the man at the scene for first- and second-degree burns, Hopkins said. The fire left both his apartment and a neighboring unit uninhabitable. Two adults and a child who live in the second apartment were displaced, Hopkins said.
An apartment on the floor below also sustained some water damage, Hopkins said.
Crews had the flames under control within 30 minutes of their arrival. The fire caused an estimated $250,000 in damage, Hopkins said.