The court heard how Whelan armed himself with a BB gun, sprayed black to make it look like a real handgun, and demanded money from staff in a series of robberies at BP, Shell, Asda and Esso petrol stations in Ruislip, Northolt and Harrow between 29 March and 18 May 2017.
In two of the Robberies Whelan had used violence by 'pistol-whipping' the cashiers with the gun to when staff first refused to hand over any money.
During the sixth offence, a piece of the gun had broken off and recovered from the scene.
The BB gun was recovered from Whelan's home address and matched the missing piece.
- Dates and locations of the robberies:
1. BP, Mandeville Road, Northolt on 29 March 2017 at 9:20pm. Whelan demanded cash from the till. Total of £170 stolen.
2. BP, Field End Road, Ruislip on 7 April 2017 at 05:55hrs. Whelan demanded cash from the till which was initially refused. He hit the cashier on the forehead with the firearm causing a small cut. Approximately £250 was stolen.
3. BP, Victoria Road, Ruislip on 14 April 2017 at 20:24hrs. Whelan demanded money and stole £668.
4. Shell, West End Road, Ruislip on 27 April 2017 at 21:16hrs. Whelan demanded money and stole £300.
5. BP, Mandeville Road, Northolt on 9 May 2017 at 21:55hrs. Whelan stole £180 after demanding money from the till.
6. Attempted robbery at Esso, Alexandra Avenue, Harrow on 16 May 2017 at 23:02hrs. Whelan hit the cashier in the face with a firearm causing bruising to his head.
7. Asda, Church Road, Northolt, 18 May 2017 at 18:35hrs. Whelan stole £738.
In total, Whelan managed to steal £2,300 during the six robberies.
Detective Constable Alan Mears, of the Met's Flying Squad, said: "Whelan is a violent criminal who used threats and violence to steal cash from petrol stations. He was committing offences at a rate of almost one a week so it was important he was caught as soon as possible."
T/Detective Chief Inspector Scott Hartley, of the Met's Flying Squad, said: "Reece Whelan committed a series of extremely violent offences, causing utter terror to members of staff working at various petrol stations who were faced with an armed man demanding cash. As a result of a diligent and painstaking investigation by the Flying Squad, a violent criminal has been brought to justice and sentenced to a lengthy period in jail."