[ponkikki]

Oh ! I am a bit embarrassed to see you go into the detail with such technical terms. You are so intelligent.
Yes, you use 脂 for あぶら in the sentence. 一番脂が乗っているのはどれですか？

and basically,
脂　for fats
油　for oils

I was not speaking of chemical terms but of daily use word(Kanji), since I thought someone who read this thread might be confused with "fish" and "fish oil".
But it seems to be apparent that I myself have been confused with "fats" and "oils". I apologize for bothering you.