I never really thought about this but recentlt I've seen some ads for Shell and BP (previously Amaco).

They both advertise their gas to have some special... crap or something that's better for cars. It's supposed to make my car faster and more fuel efficient.

So, is this true or total crap?

I've always used Mobil on my TL (because it's right in front of my house) and never really used anything else as all the gas stations have the same price.

They're all very close to the same.

I would stay away from cheap gas though, they tend to add ethanol.

some ethanol isn't all bad. it actually burns cleaner and that's the main reason for it. cleaner burning gas, better for environment. around here (iowa) the mid and high gas has 10% ethanol in it. plus since ethanol is made from corn material, we get a tax break on it. good for us, but still expensive as hell.

Yeah, our gas has 10% ethanol too.

By cheap stuff, do you mean getting regular instead of premium?

Not all gas is the same. Around here I can only choose 87/89/93 (no 91) so I usually get 89. 89 from larger stations burns well, 93 a bit better, but 89 from some of the smaller stations burns like pure crap.

i had heard a while back that Casey's gas used to be watered down some. but then i heard that the bit of moisture in the gas was good to help cool the engine (pardon? lol). so who's to know?

The basic formula of the gas is the same. The difference between the gas from different brands are what additives they put in it.

As for octane ratings, the higher the octane, the more resistance it has to ignite from compression. Using a higher rated octane gas in an engine than what it was made to use, usually will not mean that you're creating more power. The only reason you would want to use a higher octane gas is if you raise your compression ratio or if the engine is detonating.

But I take it that using a lower octane gas on a car meant to use higher octane gas hurts performance?

I need to begin using premium in my TL. Does it hurt to mix regular with premium gas? I have been using 87 since I've had it, so next time I fill up (ususally with a quarter of the tank full), can I just put in premium? Will that hurt anything (outside of my wallet)? Or do I have to do something special?

Nope. You can mix gasoline just fine.

As a matter of fact, if you mix in equal parts, you'll get the average octane of both. 1/2 tank of 87 + 1/2 tank of 93 = would get you 90 octane gas.

I don't know about the 2.5 engine in the TL, but on some Honda engines, if you put lower octane gas than its supposed to use...the engine will recognize it early and retard the timing, and thus, lower performance a bit.

http://www.straightdope.com/columns/041008.html

This guy at that sight asked basicly the same question... Sounds like the guy that responded did about a weeks research and posted his highly educated answer...

Now that i think of it... sounds kind of like Ken...

Anyways, it explains the diffrence pretty well... check it out...

The gas marketers, in conjunction with a couple major auto manufacturers, have come up with Top Tier quality ratings for gas; maybe this is what you're referring to:

Top Tier Gas

I use QT all the time because it's on my way to work.

Whether it's all hype is for you to decide

My TL has only ever had 91 octane since the day I got it from my dad (he ran 89). I ran a tank of 89 in it and did notice a SLIGHT hesitation of power when hitting the throttle hard. I ran 94 octane Sunoco in my Integra all the time, but that was because it had an 80 shot of NOS running through it. (STILL managed to melt plugs every 2nd or 3rd tank of laffin gas). As was stated before, octane usage is determined mainly by compression. As for the QUALITY of gas, that's a different story. There are a lot of "lower end" gas stations around, I have never used them myself, so I really can't say, but I have heard the RUMOURS about watered down gas, etc.