Okay. I’ve learned my lesson. I will not make any more price predictions.

Back in August 2008, I made a bold prediction. I wrote “for the next 5 to 8 years, diesel fuel will sell at a significant premium over gasoline. And by significant, I mean in the range of 15 to 30 percent.”

Today, according to the EIA, the average retail price for gasoline is $2.66 and diesel is selling for $2.78. Thus, diesel fuel is selling for a premium of about 4.5% over gasoline. But diesel contains about 12% more heat energy per gallon than gasoline. Thus, on a heat-content basis, diesel remains significantly cheaper than gasoline.

I’m prompted to foreswear further price predictions because my recent debating partner, T. Boone Pickens, is predicting that diesel prices will be much higher in the years ahead. And he’s using that prediction to justify his recent spate of TV ads calling on Congress to provide major subsidies to companies who use natural gas vehicles. When I argued with Pickens about his claim, I pointed out that the diesel market is increasingly global. Thus, any major price disparities between the foreign diesel market and the US market will be arbitraged by traders and the tankers that will follow their deals. Pickens still insisted that he was correct and that the US, in order to protect itself against future price increases in the diesel market, should push forward with more natural gas-fueled long-haul trucks.

Whatever. You can’t argue with a man whose main interest in government stems from his desire for more subsidies.

In my article from 2008, I pointed to the factors that I believed were going to force diesel prices higher. Among them: the requirements for refiners to switch their production to ultra-low sulfur diesel, the surging demand for diesel in Europe, and the IEA’s claim that soaring diesel demand was having a direct impact on global oil consumption.

All of those factors gave me a silly certainty that I was right. I wasn’t. I was wrong. And today’s prices, with gasoline and diesel selling for nearly the same price, proves that. So what happened? Well, the diesel market is getting kicked in the teeth. The lackluster global economy, flat motor fuel sales in the US, and predictions that US motor fuel demand is at, or near, its peak, along with a cooling of diesel demand in Europe are key reasons. And now, as I look forward at an increasingly global market for motor fuel, it seems obvious that US refineries have too much capacity. That helps explain why US oil exports are rising. Further, with increased refining capacity coming onstream in Saudi Arabia and India, that global trade in diesel fuel will only accelerate in the next few years.

The cooling of the European diesel market is particularly interesting. London’s Daily Telegraph reported last week that diesel cars, which have been riding a long wave of popularity in Europe, are suddenly less popular than they have been in the past. Over the past year, diesel’s share of the new car sales in Europe fell from 52% to less than 46%. There are a number of factors driving the decrease, including more stringent fuel and emissions regulations. Add in Europe’s aging refineries, which are having difficulty wringing diesel out of North Sea crude, and the price advantage that diesel fuel used to have over conventional gasoline has eroded. And that lack of price advantage has led more Europeans to buy gasoline-fueled cars. As the Telegraph’s Andrew English concluded, “Diesel isn’t dead, but it isn’t likely to grow much, either.”

In my 2008 article, I ended with a flourish, declaring that “the diesel crunch has just started. And the inflationary effects of the higher costs of diesel fuel are going to be felt throughout the US economy and the global economy for years to come.”

What I meant to say was this: I really have no idea what the future will hold with regard to prices of oil, refined products, or anything else. And this time, I mean it.