what happens when you whisk sugar with oil? So far I have tired four different carrot cakes recipes, everything ended up too oily (The oil drips from the cake when pressed). I was wondering and found all of these recipes calls for "whisking sugar with oil until the sugar dissolves" as the very first step. I am sure, I am missing some basics here, since I don't know what is the consistency needed. 

Can anyone shed light on what happens when you whisk sugar with oil? Like creaming sugar and butter to incorporate air into the mixture. What is the concept behind it? How the consistency should look?

I am using 135g white caster sugar and 100ml sunflower oil, if this information is of any help.
Oil doesn't really dissolve sugar.  The main purpose for the mixing is that in many recipe techniques, especially the muffin method, sugar is treated as a wet ingredient.  By premixing the wet ingredients, and premixing the dry ingredients, when the two are combined, you require much less additional mixing to get a homogeneous total batter.

Creaming sugar into butter or shortening helps leavening because the sharp edges of the sugar crystals cut air into the solid fat medium, essentially creating a foam.  This then serves as seed air bubbles for the chemical leavening to expand.  This effect cannot occur with liquid oils.

Many carrot cakes are pretty dense and oily, although I don't think they should drip when pressed.  You might have something else going on in your recipes or technique.