There are many reasons why your car might be using more fuel than usual. Without additional context, here are a few things that might be contributing. Is there a check engine light on? Check the codes; some things can cause the engine to burn more fuel, like a bad o2 sensor, MAF sensor, fuel injectors, etc. When was the last time you had a tune-up? If your car is really overdue for a tune-up, that can cause the engine to burn more fuel.