I "think" the 2011 tank was 12.0 Gallons, and the FiST is 12.0-12.4 Gallons? So pretty close if not favoring the ST. Could be... a few contributing reasons off the top of my head that might be giving you this result... The ST is a little more performance oriented, so it may be a little less economy friendly than the '11 you had.. (I don't know this for fact, just a guess that the ST trim gets slightly worse than the non ST trims). Also, since you were learning to drive Manual before you picked up your ST... I am assuming your '11 was automatic... Could be that your auto was slightly more efficient at shifting? (And it was also already broken in.) But this should improve for you over time. And... also, being a new car... My experience has been that my efficiency improves gradually over the duration of the first 20k miles. Both my Camaro and my Raptor improved over time as the car gets broken in. So...The bad news is that the ST is the performance version so it's probably not going to achieve what the economy trims get as far as fuel efficiency. (Luckily, the difference isn't "massive") The good news, is that... whatever you're getting right now, can probably improve in time Your car is still pretty new, and there is always room to adjust/improve driving habits to enhance your mpg.