Are diesel engines more efficient? If so why?

From Wikipedia :
“Diesel engines often achieve greater fuel efficiency than petrol (gasoline) engines. Diesel engines have energy efficiency of 45% and petrol engines of 30%.[3] That is one of the reasons why diesels have better fuel efficiency that equivalent petrol cars. A common margin is 40% more miles per gallon for an efficient turbodiesel….The higher compression ratio is helpful in raising efficiency, but diesel fuel also contains approximately 10–20% more energy per unit volume than gasoline.”

And this from http://autorepair.about.com:
“A gasoline engine compresses at a ratio of 8:1 to 12:1, while a diesel engine compresses at a ratio of 14:1 to as high as 25:1. The higher compression ratio of the diesel engine leads to better efficiency.”

This article lists the historical disadvantages that kept the more efficient diesel engine from cathing on with cars in the U.S., but says that:

“Many of the new diesel engine designs using advanced computer control are eliminating many of these disadvantages—smoke, noise, vibration and cost are all declining. In the future, we are likely to see many more diesel engines on the road.”

That’s why after years where petrol was costing almost the double of diesel now they cost approximately the same. In Europe diesel cars market share steadily grew, and exploded in the last years. I believe now more than 60% of the cars are diesel. And that is going to raise diesel price even further.