The culprits managed to manipulate the pump operated by IDS (International Diesel Service) to steal the fuel and carry out the heist according to police in Umeå.
It was an automatic pump, with the theft only discovered when a reading was done remotely in the company's Stockholm main office, showing that 40,000 litres of diesel had been stolen.
"It's not yet clear how it happened but it seems they managed to manipulate the filling station. Many others have used the pump afterwards so it is hard to establish a physical track," Michael Karlsson, duty officer with Umeå police, told local newspaper Västerbottens-Kurien.
Police have since investigated the scene in order to secure any clues. Technicians from IDS have also inspected the automatic machine to establish how the crime was carried out.
"The timing of the theft is unclear," said Michael Liljenberg, also of Umeå police, who appealed for witnesses to come forward with any additional information about the crime.
"For these kinds of crimes to be solved it requires close observation or camera surveillance," he added.
Last year, seven men were arrested on suspicion of aggravated robbery and weapons crimes after a truck driver was beaten and robbed of 450 litres of diesel fuel at a rest area north of Gothenburg, western Sweden.