There are many products on the market designed specifically for acne prone skin. Acne sufferers are advised to look for non-comodogenic moisturisers ie ones that are not oily and greasy. Many people find it difficult to get a moisturiser that works with their skin rather than against it. As a result, people look for options outside those specifically for acne.
One such option people consider is the use of petroleum jelly. We see the effect it has on sore chapped lips and 'granny like' elbows so why wouldn't it help our faces?
Well, as with most things pertaining to acne, it's basically down to trial and error on your part. For some people their skin will break out but for others they find it helps. The main point to note is that it really isn't a substitute for a moisturiser as part of your acne skin care regime. It works to seal in whatever moisture your skin already has. Many people find moisturising their skin then applying petroleum jelly helps the skin lock in as much moisture from the moisturiser.
The only way you'll know if it is effective for you is to give it a go. If you have used it before you'll know it's greasy looking and absorbs slowly. Try putting it on at night and feel your face the next morning ... remember to sleep on your back!