What will cause my buick Rainier to get low gase mileage. on 2006 Buick Rainier

What will cause my buick Rainier to get low gase mileage. I currently get 10mpg on highway?

Asked by for the 2006 Buick Rainier
1 answer
That is to broad of a question. How many miles on vehicle? What have you done as far as servicing the truck? I don't mean just oil changes.