The number of gallons of gas used to power a car for 1,000 miles depends entirely on the fuel economy of the car.
For example, if a car only gets 20 miles to each gallon: 1,000 miles/20mpg = 50 gallons.
However, if the car were to get 50 miles to the gallon: 1,000 miles/50mpg = 20 gallons.
You can figure this out for your car by looking up the average miles per gallon your car gets, and then dividing that into 1,000; the result will be how many gallons are needed.
Although it doesn't consume gas, the new Honda Fit EV set a record for MPG; according to the EPA the 2013 all-electric Fit achieves an equivalent of 118 miles to the gallon.
That means that if it did use gasoline it would need less than 8.5 gallons of gasoline to travel 1,000 miles!