Detectives are appealing for witnesses after a robbery at the BP-branded Parkwood Service Station, Maidstone, Kent, on Wednesday 9 March, at around 8pm.
The robbery happened after a man entered the shop and shouted at staff to open the till.
He then reached across the counter and managed to open the till himself. It is alleged that he was seen to be holding a knife at the time.
A quantity of cash was stolen before he fled through an exit in the direction of Wallis Avenue.
The robber was described as wearing a distinctive white onesie with black spots.
A 24-year-old man from Maidstone has been arrested in connection with the incident and has been bailed pending further enquiries until 6 April, 2016.
Officers are appealing to anyone who may have seen anything suspicious to get in touch.
Anyone with information should contact the appeals line on 01622 604100, quoting reference YY/5310/16. Alternatively, they can contact Crimestoppers, anonymously on 0800 555111.