Surveillance video showed the latest robbery on Sunday morning.
The armed man stole cash and cigarettes from a Citgo gas station on Jericho Turnpike in Mineola.
Police believe this is the same suspect who robbed six stores in Nassau County last Thursday and Friday.
The stores were in Farmingdale, Levittown, Hicksville, Roslyn Heights, Flower Hill and Great Neck.
All the incidents happened between 3 and 4 in the morning.
The county police robbery squad canvassed the stores for witnesses and surveillance video.
Although the robber has threatened clerks, he has not fired a single shot, at least not so far.
No injuries have been reported.