Dallas police say distracted drivers are easy carjacking targets.
Police report more than three dozen carjackings since the start of the year.
Erin Adams, 30, the latest carjacking victim, said the robber came toward her just as she was pulling the pump out of the tank of her Hyundai Accent.
"I guess I wasn't paying attention the way I should have," she said. "All of a sudden, this man approached from behind the building with a switchblade."
"All he said was, 'Don't scream. Give me your keys,' over and over again," Adams said.
Of the 37 carjackings in Dallas so far this year, 24 have involved a weapon.
"If he wanted to, he could have stabbed me with the knife," Adams said. "There was nothing there preventing him."
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It happened at about 11 a.m. at the Exxon On the Run at the intersection of Mockingbird and Greenville in East Dallas.
"Anytime anyone does something like that in broad daylight, while someone is just putting in gas -- that's unusual," Lt. Andy Harvey said.
But police said drivers should pay attention to what's around them. Adams said she "sure will" be more aware in the future.
"I should have been watching better than I was," she said. "You should really be more aware of your surroundings."
Police said the man who stole Adams' car was wearing a one-piece tan jumpsuit, similar to what a mechanic would wear, and carried an empty gas container.
Investigators are reviewing surveillance video of the incident.
