It's the fuel that keeps Pawtucket city vehicles running, paid for with tax dollars.
But the NBC 10 I-Team has learned someone within the city may have used the city's gas pumps to fill up a personal vehicle instead.
Multiple sources told NBC 10 that part of the investigation is focused inside the police department.
Calls and emails to the department were not returned on Friday, and the mayor's office isn't commenting on who may be involved in the investigation.
Only city employees who drive city vehicles have access to the gas.
The pumps are located in a restricted area that requires a key card to enter, with gates that lock after business hours. Once inside, employees have to enter both a vehicle number and ID number on a keypad.
It wasn't immediately known how much gas might have been taken, and how long it had been happening.
"The city of Pawtucket became aware of potential issues involving possible misuse of the city gas pump at the Department of Public Works. The pump, to which access is limited, is for official use only. There is an ongoing investigation to determine if any such misuse has occurred and if so, to what extent," Director of Administration of Public Safety Antonio Pires said in a statement.
There are 303 city vehicles eligible to gas up at the pumps. They include, the Department of Public Works, the fire department, the police department, the library, the senior center and the zoning department.