The whole field of oil additives and fuel economy enhancers has me confused. If they work, why hasn't the world beaten a path to their door? Especially now, with fuel prices at unprecedented highs.

Fuel prices are expected to continue up - possibly to more than $4 a gallon, if the pundits are right. (And I'm about as skeptical of pundits as I am of fuel additive claimants.)

But maybe this fuel crisis is what it will take to propel skeptical users to take a look at fuel economy enhancers.

I happen to know there's one major truckload carrier taking a very serious look at Go-15, an oil additive whose name tells the claim: up to 15 percent fuel economy improvement.

Now, I have never believed a 15 percent improvement in economy is possible. But Go-15's prospectus and promotion say it is. And many user testimonials claim that treatment of vehicles in their fleets with Go-15 has achieved such remarkable fuel economy gains - even more.

And these Go-15 people are very persuasive.

In fact, they tend to downplay the results. But company president Jim Novorr is absolutely confident that no one will see less than an 8 percent gain in fuel economy when using their product.

You don't need me to tell you that's huge. For the truckload carriers, this year is going to be tough. We have seen predictions that margins are going to be eroded from the 4 percent of 2007 to as little as 2 percent for 2008. With fuel accounting for 33 percent of costs, an 8 percent saving could wipe out that loss. And a little bit more.

Go-15's marketers claim it's a surface conditioner, treating sliding surfaces so the metal-to-metal friction is lower. Talk to lubricant engineers and they'll tell you metal-to-metal contact is zero because the oil film maintained by conventional mineral - and especially synthetic - lubricants is there to prevent exactly that.

But it's hard to argue the oil analysis results that the Go-15 people lay in front of you: The amounts of wear metals in successive oil samples before and after engine treatment show significantly lower numbers for iron, lead, zinc and so on - all indicators that something is going on inside an engine that is minimizing the contact between sliding metal components.

Subjective comments support the notion. Truck specifiers I know and respect say engines idle more smoothly, transmissions and axles are quieter. One Harley distributor says heat transmission through the seats of the bikes is significantly reduced.

And the micrograph analysis on metal surfaces tends to back this up. The surfaces under extreme magnification show a much smoother, less jagged appearance. And lest you doubt the claim, the source is the highly respected Southwest Research Institute, the same body that oil companies use to qualify their lubricants to meet API "doughnut" standards.

But in reference to the oil companies, I have to offer a cautionary word from my friend and colleague George Morrison, founder of AV Lubricants in Columbus, Ohio, who a few years ago helped author our award-winning feature on fuel filtration, "Trucking's Dirty Little Secret."

"From my experience with additives, there is just no free lunch," he writes. "There are additives that appear to be the greatest stuff since sliced bread, but in every single case some major oil producer had already researched the component and found that the additive produces side effects in the long term or some other component that makes the additive not cost effective. ExxonMobil, for example, has a research lab in Paulsboro, N.J., where a whole gaggle of Ph.Ds do nothing but try and re-invent the wheel in terms of energy-saving additives."

So he's a skeptic, too.

But it's not the promoters, it's the people who use Go-15 who seem to be such believers. It's tough to ignore their enthusiasm.

Try an Internet search for Go-15 (note the hyphen), see their claims, and you can decide for yourself. With fuel prices sky high, it might be worth a shot. Even for this skeptic.