I am getting a smell of gas when the car has been driven and parked. If it has just been setting parked no smell. Only after it has been driven. Smell is near the rear passenger side of car. Bad mileage. It is a leak. But I'm not sure from what. Can you help?

Let the engine idle in the driveway and look for the leak it will probably drip to the ground. Don't smoke while looking!

You may have rusted fuel pipes or loose fittings.
Unless someone has recently attempted maintanance or repairs, you likely have rust.
Before starting the car, look under the area where you suspect a leak. Look for any signs of fuel: washed clean or still wet.