Abstract: Methods and systems for detecting a leak in a compressed natural gas (CNG) delivery system of a vehicle are disclosed. According to some embodiments the method includes determining a first amount of CNG in a CNG tank of the vehicle, the first amount corresponding to a first time, and determining a second amount of CNG in the CNG tank at a second time, the second time being subsequent to the first time. The method further includes determining an expected CNG consumption of the vehicle during a period of time, the period of time beginning at the first time and ending at the second time. The method also includes determining an actual CNG consumption during the period of time based on the first amount of CNG and the second amount of CNG, and comparing the actual CNG consumption and the expected CNG consumption to determine whether a leak has occurred.