The Great American Gas Swindle Revisited

I had another rather grumpy commenter drop a line on this vintage posting: The Great American Gas Swindle.

Unfortunately, he hadn't read the follow-up, Taking a Spin in the No-Fact Zone, which addressed the issue he and another commenter had raised regarding some of the facts [All of the facts, actually - Editorial Bear] I'd mentioned.

The issue they were discussing was the difference between European and American petrol.

I had quite reasonably assumed (based on the numbers on the pumps and a misleading Wikipedia entry) that the gasoline sold in America was of an inferior 'Octane Rating' than the petrol sold in the UK and mainland Europe.

Specifically that American gas is sold in Regular (87 Octane) Premium (89 Octane) and Super (91 Octane) varieties - all of which seem inferior to European petrol, which is sold at 94 Octane (Unleaded) or 98 Octane (Super Unleaded.)

The 'Octane' rating references the 'knock resistance' of an engine, or the likelyhood of 'Auto Ignition' which could cause 'knocking' or 'pinking.' That's the rattle in the engine that indicates the fuel is igniting early and causing your pistons to fire out of sequence (damaging your engine.)

Based on my previous information, it's very simple to assume that American petrol had a lower Octane rating (and was of inferior quality) to European fuel.

However, I have been informed that America and Europe have different ratings systems to determine the Octane Rating of their fuel. The Europeans (and most of the rest of the world) use the Research Octane Number (RON) to determine the Octane Rating.

The Americans and Canadians apparently use a measuring system called Motor Octane Number (MON) or the aviation lean octane rating - which is a similar, but more stringent test using pre-warmed fuel and variable ignition times to deliver an accurate Octane rating based on more demanding criteria.

Because the MON test is 'harder,' the Octane Ratings derived that way tend to be about 4 or 5 points lower than the equivalent European RON tests. Therefore, 89 Octane American fuel (sold as 'Premium') would actually be equivalent to regular 94 Octane Unleaded sold from European pumps.

So when it comes down to it, European and American fuel is actually pretty much the same stuff... Or is it?

There's one more important factor to consider. Across much of the United States (mandated by law in some States) the oil-based fuel sold in petrol stations is actually mixed with 10% corn-based ethanol.

This increasingly common trend is intended to help reduce America's reliance on foreign oil - and the percentage of ethanol mixed in with regular petrol will only increase as technology helps close the net energy unbalance of producing corn-based fuel.

One thing to remember about corn-ethanol based fuels is that they're about 35% less efficient than regular petroleum. Therefore, even the 10% mix in American petrol is enough to reduce your overall fuel consumption.

So while I might have been wrong about the RON and MON ratings, it's still worth remembering that what goes into your tank in America still won't get you as far as it will in Europe (and that's ignoring that fact that your American car only does 15mpg!)