how old is the car ? .... well maintained ? ....
lots of things would help .... from the exhaust to the air filter,
fuel filter, fuel pump, engine oil, oxygen sensor, spark plugs etc
....
go round to the back of the car and sniff at the exhaust a bit, got
strong gasoline smell ? .... that may imply that the combustion is
not happening properly, or more than the required fuel is being
injected ...