I've used coconut oil this entire pregnancy!
Just ran out of the first bottle I bought a couple of weeks ago. It lasts for AGES. I don't have any stretch marks so far this time around (30 weeks now).
That said I only wound up with 2-3 stretch marks from my previous 2 pregnancies. I've never noticed any on my mom, but she only gained 20 pounds and I'm an only child so she doesn't count. LOL I think the most important thing is to moisturise like crazy. I don't think it rally matters that much what you use, as I've used Palmer's cocoa butter, bio oil and olive oil as well in the past. Just pick something that smells good and that you enjoy rubbing all over your bump and bum and boobs and use it constantly!!
Also, don't neglect you're calves. My worst stretch mark is on the back of one of my calves!