The robbery was reported at 10:06 a.m. in the 1100 block of Junipero Serra Boulevard, according to police.
The suspect, described only as a black man between 35 and 40 years old, entered the gas station's store, selected some candy, and handed it to the female employee at the cash register, police said.
The suspect then handed the employee five dollars, but when she opened the cash register, he pulled out a gun, hopped the counter and took money from the register, according to police.
The suspect then fled in a car and had not been arrested as of this morning, police said.
The employee, a 55-year-old woman, was not injured during the robbery.