Police say the raiders, who all had their faces concealed, entered the service station's shop at 12.50am.
They then helped themselves to large quantities of cigarettes from behind the counter before leaving in a silver BMW.
Esso was open at the time but the shop assistant was not threatened or harmed.
The petrol station was closed this morning as police forensic teams gathered evidence but re-opened this afternoon.
Police are appealing for anyone who saw a silver BMW in the Braywick area to contact them by calling 101.
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The victim of an assault in Cippenham was flown to hospital by air ambulance this afternoon.
A rapid response vehicle, an ambulance officer, an air ambulance and an ambulance crew were all called to an address in Earls Lane at 2.10pm.