A cake recipe of mine calls for ½ cup of Vegetable Oil Spread (Specifically stating 70% fat), which I don't currently have.  I found questions that deal with substituting either Butter for Oil, Oil for Butter, and Butter for Margarine and have read their answers.  However, despite now being able to extrapolate how likely substituting (which I think is the best alternative) Oil for (What is understand is) the Margarine-like product called for in the recipe, I found no questions/answers that address this swap specifically. Am therefore keen on the communities opinions on which is the best substitute, why and any caveats? 
In the US, to be labeled as margarine, the product must contain 80% fat per the Standard of Identity.  The spread simply cannot be called margarine.  However, with a fat content of 70%, it is quite close to a standard margarine, and is likely otherwise the same thing.  Almost all recipes have enough tolerance that you could substitute regular margarine, real butter, or another vegetable oil 1:1.  If you want to be more exact, you could approximate pretty closely (for easier math) by just using 3/4 the amount of a 100% fat product like shortening or vegetable oil, or 7/8 as much margarine or butter. 