Question: I was wondering if "An" should be used with *obligatory* or "A". I understand that since *obligatory* begins with a vowel I should use "An" but I see people are using "A" more frequently than "An"

To me "A obligatory like" sounds right, as in "a Facebook like".

Also .. Is "and a obligatory comment" correct or is it "and an obligatory comment" ?

Answer: 
To me only "an obligatory" sounds right. "a obligatory" is not only more difficult to pronounce but also sounds pretty odd (to me at least). [Google ngram](https://books.google.com/ngrams/graph?content=an%20obligatory%2C%20a%20obligatory&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Can%20obligatory%3B%2Cc0%3B.t1%3B%2Ca%20obligatory%3B%2Cc0) seems to agree with me:

![Google Ngram](https://i.stack.imgur.com/HH7xb.png)
I think an important point is that you "see" this but it "sounds ... unnatural".

The pronoun was invented for pronunciation. It prevents the speaker from having to separate the vowels.

Since it is not necessary to speak while typing, I suggest that "a obligatory" is an Internet artifact.