If they're independently owned/operated, my guess is BP corporate policy may not be relevant and the franchisee is the one responsible for permitting or banning guns.
Here's thee-mail I sent:
To Whom It May Concern,
Does BP have a corporate policy regarding the lawful carrying of firearms in it's convenience stores/gas stations?
I ask, because I was recently informed of a situation in which a gentleman in Dickson, Tennessee was told that he could not come into the store (Store #3) with his openly-carried firearm. As a 2nd amendment supporter, I am happy to support and patronize businesses that allow their customers to exercise their constitutional rights, and hope that BP feels as strongly regarding an individuals right to self-defense as the hundreds of thousands of U.S. citizens with licenses to carry firearms.