What weight of oil do you use on a 2003 Jeep Liberty sport 4x4?

Always go by the manufacturer's recommendations in the owner's manual. That being said, the manufacturer recommends different weights of oil depending on climate and use. I always use 5w30 because it fits within the temperature range here. You can also use 10w30. Always change your oil filter when you change your oil. The best filter I've found for quality and price is the Motocraft 400s Filter.