i'm not familur with bj's but im assuming just generic gas in general. my experience with gas in my car is this. i drive 90miles a day in my car minumim. i've used most major top tier gasses, and a few generic's. i always recieve lower miliage from the top tier gases. i'm not sure if its the additive's and cleaners or what, but i fill up 90-95% of the time from a little marina gas station just outside the neighborhood and consistantly pull 27-30mpg with mixed driving. stores like shell, cheveron, and exxon, it will drop into the 25mpg range. i'll keep using the marina store. and no its not boat gas, just the name of the station.