I have put on a combined weight of 79kg's (over 3 pregnancies), and have 2 stretchmarks on each hip. Absolutely none on my stomach! I also have olive skin, which is prone to scarring.

Here is what I used. I mixed this myself.
Extra Virgin Olive Oil (the greener it looks, the better!)
Collagen oil (difficult to obtain and quite expensive, but you use a little, so it really goes a long way)
Bio-Oil (Vit E with PurCellin)

Mix two parts Olive oil with one part VitE oil, then add 10 ml of Collagen oil.
Use twice a day, and especially before you sleep. You need to use your old sheets, or they may stain.

It worked for me, even though my husband said that I smelt like a greek salad all the time! LOL