It's 2.0 million barrels per day.  Choose the short form you like, just choose one that someone else somewhere uses and makes some sense - i.e. stop putting slashes immediately after the number.  Personally I like Mb/d, but that's because I happen to think metric prefixes make sense.

This may seem petty, but in one of your other excellent posts you had this, and other unit confusion, littered throughout, and it really detracts from the article.  It's not just me saying this, other people I have referred to the article have said the same thing.