Why the car is consuming more fuel

A more detailed question should be asked. What type of engine. Is the check engine light on. When is the last time you had a tuneup? My guess is never...

Double the fuel consumption you either have drag (issue with the brake system, seized calipers), sensor(s), fouled plugs, air filter clogged, vacuum leaks, a fuel leak, under inflated tires. Although it won't be a tire issue..

My guess is start with a tuneup, plugs, filter etc..