In the Owners manual is stated:
For better fuel economy, it is recommended to use the engine oil of
a viscosity grade SAE 5W-20 (API SM / ILSAC GF-4). However, if the engine oil is not available in your country, select the the proper engine oil engine oil using the engine oil viscosity chart.
What brand of oil to use is up to you. Castrol 5W-20 GTX, Pennzoil, Valvoline, or you can go up to Mobile 1, which is more expensive. If you change oil every 3000miles or 3 months, then you may not use synthetic oil, but it is up to you. My personal opinion is:
It is better to change 5W-20 Castrol GTX every 3 months or 3000miles than fully synthetic Mobil1 5W-20 every 6months or 6000miles.
You can use 5W-20 all year around, but when you Kia Sorento will accumulate miles, and engine start to wear up, thicker 10W-30 is a suitable substitute. If the temperature will be 20F and expected to fall you must not use 10W-30, and will have 5W-20 in your Kia Sorento Oil PAN. The reason is that, when you start the engine the oil is in the Oil Pan, and 10w-30 is very thick in low temperatures. Till the oil warms up the engine wears up extensively.