Police are investigating an aggravated robbery at the BP On the Run service station on Bridge Road, Pooraka overnight.
Hold-up alarms were activated at 1.58am when a man forced his way through the security doors and threatened staff.
He was allegedly armed with a screwdriver and stole a small amount of cash.
The offender is described as Caucasian, slim build and wearing black jeans, black sneakers with white laces and soles, a blue cap, black hooded top and a white mask.
He had a red sock on his right hand and was last seen north on Bridge Road.