One example to make the point: We were approaching the Arc de Triomphe intending to go into the roundabout and come out the opposite side. The roundabout has six chaotic lanes and 12 radiating streets, so it would seem obvious that getting into the outside lane, circling right and slipping out again made good sense. Not so! Instead, the cabbie gunned his engine and went straight across. No lanes, no concerns about speed limits – just straight across. Since Im writing this, you know we made it. However, I do have bruises on my arm where my wife gripped it as we shot across.

So here I am in Paris, and what am I looking at? Automobiles! They are predominantly French (no surprise) and include many Peugeots and Citroens. In fact, our cabs typically were one or the other, and equipped with diesel engines and manual transmissions. I was truly impressed with the vehicles performance, including their acceleration (a life-saver) and quiet operation. They raised some questions in my mind about diesel-powered passenger cars in the United States.

Other than a brief period during the 1970s fuel crisis, diesels have never been popular for U.S. passenger cars. In Europe, Volkswagen is the biggest car company and 60 percent of the cars it sells on the continent are diesel. And its not just a German or a VW thing. More than half of all cars sold in Europe are diesel – Mercedes, Ford, BMW, Toyota, Renault, Opel, you name it. Even the Mini Cooper and the Smart come in diesel versions.

Why this popularity? It starts with fuel taxes. Diesel vehicles produce lower CO2, hydrocarbon and NOX emissions; therefore the taxes on diesel fuel have been lower than for gasoline in most of Europe since the early 1990s. Diesels also offer better mileage and longer engine life. Fuel is much more expensive in Europe, so anything that improves fuel economy has strong appeal for drivers.

So why didnt diesel-powered cars become popular in the United States, apart from the lack of tax incentives? Five negatives are stuck in consumers memories: Diesels are heavier. Diesels cost more than a gasoline engine of equivalent horsepower. Theyre noisier. The exhaust smells. Diesel fuel is less readily available than gasoline.

Diesel fuel also costs more than regular gasoline in the United States, so the pump price is another negative, although diesels can offset that with better mileage. But today, technology advances mean that a diesel is no longer the same noisy, smelly beast that turned Americans off in the 1970s.

U.S. OEMs continue to look at diesels as a way to reach the stricter Corporate Average Fuel Economy requirements coming in 2016 and beyond. At the APIs 2010 Detroit Automotive/Petroleum Industry Forum, Ford executive Barb Samardzich indicated that diesel engines will have an even larger place in its global mix for improved fuel economy, from roughly 40 percent now worldwide.

However, if youre waiting for Ford to release a diesel-powered Fiesta, Focus or Fusion in the United States, dont. According to a recent article in Wards Auto World, Ford has no immediate plans to bring diesel cars to North America, despite offering turbodiesel engines nearly everywhere else in the world.

Cost is a major consideration. Certifying a diesel engine for sale in the United States is expensive, since we currently have the worlds strictest emission standards for diesel passenger cars. Thats a high barrier to entry. If you cant charge a significantly higher price for a diesel engine option in the U.S., going though the motions of having one certified is a losing proposition.

Chrysler has made some inroads into diesel power. Its U.S.-specification Jeep Grand Cherokee will get a diesel option in 2013, with other large Chrysler vehicles to follow, Fiat/Chrysler CEO Sergio Marchionne told Automotive News recently. In Europe, the Grand Cherokee has the option of a VM Motori-produced 3.0-liter turbodiesel V6 engine, producing 224 horsepower and 406 lb-ft of torque. This engine also is offered in the Euro version of the Chrysler 300. This engine could find its way into North American Chryslers in the future, but no announcements have been made.

General Motors has confirmed a diesel-powered version of the Chevy Cruze is coming in 2013. It will start building these – the companys first diesel-powered passenger car for this market in more than 20 years – at the Lordstown plant in Ohio.

The Cruze diesel already is sold in Europe and Australia, and is powered by a 2.0-liter turbodiesel four-cylinder with either 127 hp and 221 lb-ft of torque, or 163 hp and 265 lb-ft. While the gasoline-powered Cruze Eco sold in the United States gets an impressive 42 mpg on the highway, the diesel Eco-D version could achieve close to 50 mpg, per preliminary GM estimates.

A Cruze diesel would be a big deal, and not only because it would be Chevys first diesel passenger car for this market since the Chevette in the 1980s. It also would be head-on competition for VWs Jetta TDI, the Cruzes closest diesel car competitor. Diesels have been embraced by Volkswagen customers and now account for 20 percent of VWs sales in the United States.

Of course, with effort U.S. drivers can buy passenger car diesels. In addition to various VW models, they can choose from Audi, Mercedes-Benz and BMW. And theres always a big diesel-powered pickup if you just have to have a diesel and dont like any of those.

If U.S. drivers can get comfortable with diesel again, a growing question will be what oil they should use. Our current engine oil system doesnt address passenger car diesels, only heavy-duty ones. Lacking a light-duty category under API, it seems likely that vehicle OEMs will dictate to a great extent what engine oils they want for these diesels. Heres what we have so far:

GM has already developed an engine oil specification for all its diesel engines, the trademarked Dexos2, which includes SAE 5W-30 and 0W-40 for factory fill, and 5W-30, 0W-30, 5W-40 and 0W-40 for service fill. Note the absence of the classic heavy-duty SAE 15W-40 grade, traditional for North American diesels.

In addition to standard ASTM gasoline engine test protocols, Dexos2 requires many engine tests from Europes ACEA. These tests help to guarantee Dexos is a truly global standard, and open the door to European diesel engines being imported for use in North America.

The current Ford diesel spec is WSS-M2C171-E. This is an API CJ-4 oil, covering all viscosity grades. There is a separate factory-fill spec, WSS-M2C206-A, calling for SAE 10W-30 only, the grade Ford uses for diesel factory-fill. Given that the only Ford-designed and -built diesel engines in the companys line are for their pickup trucks, this is not surprising. If Ford does introduce a U.S. passenger car diesel, it will probably utilize its European designs and the oil specification will conceivably look more like Europes ACEA requirements.

As with Ford, Chryslers diesel engine oil spec is API CJ-4 in appropriate viscosity grades. Currently, its diesel line-up is mainly pickups for heavy-duty use (think Dodge Ram). Given Marchionnes statements regarding diesels for the U.S. market, it seems likely that Chrysler will also require engine oils similar to those in Europe.

North Americas next diesel specification (known so far as PC-11) is apparently going to include a lighter viscosity grade (likely SAE 5W-30) which would be a natural for passenger car diesels. Its proposed for introduction in January 2016, and will have the engine performance and viscometrics needed to give good fuel economy and protection.

From a small base, passenger car diesels could make big inroads by then. Will the lubricants industry be ready for it? Auto industry research firm R.L. Polk says that diesels and hybrids now are about dead-even in terms of U.S. market share. The first quarter of 2011 showed sales of diesels at over 71,000 vehicles (2.3 percent of sales) while hybrids were at about 80,000 (2.6 percent). Not big numbers for either, however both showed an almost 20 percent increase over first-quarter 2010 sales.

So if hybrids and diesels are equally popular and diesels have better fuel economy than gasoline engines, think how a diesel hybrid would look. I saw those in Europe, and maybe someday Ill see them in North America too.

So thats my vacation story. Paris cabs are like Disney World thrill rides, and theyre an interesting way to get around the city. I recommend Paris as a vacation destination, and have pictures to share if youre interested.