A method for determining an extra-fuel consumption of a terrestrial vehicle, in particular a commercial or industrial vehicle, comprising at least the following steps in succession: - Step 1: a first acquisition of at least. a first set of input parameters related to environmental and mission conditions,. a second set of input parameters related to vehicle specifications and. a third set of input parameters related to a vehicle driving style; said driving style meaning those conditions under which the vehicle is used by the driver; - Step 2: estimating a first expected fuel consumption in time, based on said first, second and third set of input parameters, - Step 3: a second acquisition of a measured fuel consumption in time, - Step 4: comparing, preferably in real time, said expected fuel consumption with said measured fuel consumption, thereby obtaining an error value in time, - Step 5: checking: whether said error value increases abruptly, if so - Step 6: activating a flag indicating an extra-fuel consumption condition; - Step 7': a third acquisition of a fifth set of input parameters related to an ideal vehicle driving style; said driving style being based at least on: average time of use of the cruise control, driving style score, both positive and negative accelerations of the vehicle, the frequency of use of the brakes, the use of the Stop&Start; - Step 2': estimating a second expected fuel consumption in time, based on said first, second and fifth set of input parameters; - Step 9': carrying out a comparison between said first and said second expected fuel consumption and if there is an offset greater than a predetermined threshold, then a cause of extra-consumption is identified as an incorrect vehicle use; determining a cause of the extra-fuel consumption, performed when said flag is active, comprising the following steps in succession, possibly, parallelly to and independently of said steps 7', 2' and 9': - Step 7: a fourth acquisition of a fourth set of input parameters related to stored records relating to events concerning abnormalities and variations in the operating conditions of the engine and/or vehicle, - Step 8: checking: whether at least one record is present, if so - Step 9: the instant of registering said record, respectively each of the records, is compared with said activation of said first flag so as to identify a cause-effect relation between the abnormalities or variations of the registered operating conditions and said error increase. - Step 1: a first acquisition of at least. a first set of input parameters related to environmental and mission conditions,. a second set of input parameters related to vehicle specifications and. a third set of input parameters related to a vehicle driving style; said driving style meaning those conditions under which the vehicle is used by the driver;. a first set of input parameters related to environmental and mission conditions,. a second set of input parameters related to vehicle specifications and. a third set of input parameters related to a vehicle driving style; said driving style meaning those conditions under which the vehicle is used by the driver; - Step 2: estimating a first expected fuel consumption in time, based on said first, second and third set of input parameters, - Step 3: a second acquisition of a measured fuel consumption in time, - Step 4: comparing, preferably in real time, said expected fuel consumption with said measured fuel consumption, thereby obtaining an error value in time, - Step 5: checking: whether said error value increases abruptly, if so - Step 6: activating a flag indicating an extra-fuel consumption condition; - Step 7': a third acquisition of a fifth set of input parameters related to an ideal vehicle driving style; said driving style being based at least on: average time of use of the cruise control, driving style score, both positive and negative accelerations of the vehicle, the frequency of use of the brakes, the use of the Stop&Start; average time of use of the cruise control, driving style score, both positive and negative accelerations of the vehicle, the frequency of use of the brakes, the use of the Stop&Start; - Step 2': estimating a second expected fuel consumption in time, based on said first, second and fifth set of input parameters; - Step 9': carrying out a comparison between said first and said second expected fuel consumption and if there is an offset greater than a predetermined threshold, then a cause of extra-consumption is identified as an incorrect vehicle use; determining a cause of the extra-fuel consumption, performed when said flag is active, comprising the following steps in succession, possibly, parallelly to and independently of said steps 7', 2' and 9': - Step 7: a fourth acquisition of a fourth set of input parameters related to stored records relating to events concerning abnormalities and variations in the operating conditions of the engine and/or vehicle, - Step 8: checking: whether at least one record is present, if so - Step 9: the instant of registering said record, respectively each of the records, is compared with said activation of said first flag so as to identify a cause-effect relation between the abnormalities or variations of the registered operating conditions and said error increase.