what oil is used in the 2005 chevy cavalier

Conventional or synthetic is a personal choice, your Cav will be fine on either, synthetic lasts longer between changes but is much more expensive. Check your owners manual, or if you don't have it and one of the guys here does not know and post whatever it calls for, you can't go too far wrong with 5W/30 of either kind of oil. Buy a good filter, they are not all the same..not at all. Wix for example is good. Cheap filters with cardboard filtering mediums not only do a lesser filtering job they restrict oil flow.

5W-30 recommended by manufacturer, Synthetic is a matter of choice but most are coming with synthetic from the factory now. Oil change interval is best at 3000 miles or 5000 kilometres , as an engine builder i recommend synthetic and a good one is Mobile 1 . Synthetic is more expensive but it also takes heat and cold a lot better and doesn't break down so easily as conventional oils so is worth the extra money in my books

I would think that an engine builder would know how to spell Mobil oil. Don't believe ya!

Well luckily he wasn't trying to make you believe anything.

I use Mobil 1 5W30 every 3000 miles. It has never let me down.