What oil should I use?
 

My car is a 2006 Kia Rio LX with 26,500 miles on it. I drive about 24k miles a year, at least 75% being highway miles.

It says to use 5w20 oil in my manual. However, I heard that synthetic gets better gas mileage, is this true? Also, what's a good brand? I heard Amsoil is good. Should I stick with 5w20 or go down to 0w20 with the synthetic oil? Finally, how long should I go between oil changes?

Sorry for all the questions...
Thanks in advance!!

If you go synthetic, don't play around and just go with mobil1EP. It's not like mobil's or others plain synthetics. Mobil 1 Extended Performance

Switching to synthetic may be a good idea, but it doesn't allow you to switch to a lighter weight. Stick with the lightest that the manual recommends.

Thanks for the info!

Synthetic oil changes should go no less than 5,000 mile oil change intervals. Any sooner is a waste of money.

That's what I thought, thanks Johnny Mullet!

if you had a car with a real oil pressure gauge then you would run the thinest oil that let you keep your oil pressure up high enough to keep your crank bearings suspended in their cushion of oil, without this gauge you can kind of guess by telling how soon it takes for your oil pressure light to come on after switching the engine off in a coast, in the winter mine holds pressure for almost 7 seconds with 0w 30 oil, in the summer it holds pressure for almost 2 seconds with 0w 30 and 3 or more with 10w30 synthetic, being a new engine that should be broken in, I would say 0w 20 might work as long as it doesn't cause any problems, if you aren't sure then don't do it, it's that simple, if you are willing to take responsibility to make sure everything is ok, then do it.