I want to know how much good is my gas mileage on my 1998 malibu LS

If you want ot know what gas mileage your car is actually getting, do this.

Fill the tank all the way up. Record the mileage on the odometer. As an example, lets say it's 100,000 miles. Drive the car normally, use up most of the tank.

Fill it up all the way again. Record how much gas you needed (from the gas pump) to fill it. Record your mileage now.

Lets say mileage is now 100,500 and it took 20 gallons to fill.

That's 500 miles using 20 gallons, or 25 miles/gallon average. Do this a few times to get the best average.

I have a 2000 malibu ls, and it gets about 27 in city to about 32-34 on open highway.