Excessive gas consumption or just me?

I would smell the oil to see if it has gasoline in it. Do an actual fuel economy test rather than relying on gauges. Fill it up, write down the miles, drive it and then fill it again and write down the gallons and miles. Calculate the economy by dividing the miles you drove by the gallons it took to fill it the second time.

22mpg is not bad. Your car is rated 27 highway, 17 city.

I purchased a 2010 Buick Lucerne CXL sedan, I'm only getting 350 to 400 kilometres to a single tank of gas. Before this I had a 4 cylinder 2003 Toyota Camry XLE with this sedan I got extremely good fuel mileage. To do the front brake pads, 4 brake rotors was $1,400, I've already replaced one of the catolic converters (this Buick has 2 of them), I replace all 4 tires with Michelin all season tires. My vehicle only has 157,000 kilometres on it. I've only driven it 10,000 kilometres since I've oven it & already I've spend $9,000 in repairs. This is not a reliable vehicle at all. Buy a Toyota Camry, Toyota Avalon, or a Lexus IS 300 RWD or AWD, or the F Sport series & you will be making a way better choice than buying a 2010 Buick Lucerne CXL sedan.

Old school Buick Park ave,Le Sabres,ect (97-05) has the bullet proof 3800 engine. More durable and reliable than Toyota,Honda,ect. Timing chain vs a flimsy timing belt makes a huge difference. What's "good" gas mileage when your engine locks up? I'd rather sacrifice some fuel economy than a $3,000 engine any day!