There's a bit more to the story. Tires with low rolling resistance use slightly less fuel than normal tires of the same size. The first low resistance tire on the market was the original Continental EcoContact. Conti decided that 7% silica in the tread compound was the best compromise between performance and fuel savings. As other tire makers entered this market segment, they thought that if 7% silica gave some fuel savings, then 14% would double the savings and 21% would triple them. That idea was more-or-less correct and soon almost everyone had an energy-efficient tire on the market. Michelin and Dunlop in particular jumped on the "more-is-better' idea and introduced tires with much more silica than Conti used. They did get better fuel savings, but they paid for it with lower performance, especially in the wet.
Conti is now on the third generation of the EcoContact and the others have also moved along as well. Conti still uses less silica that most/all of its competitors as they believe that performance should not be sacrificed to economy.
On my last installment, I mentioned the difference between hard and soft tires but I did not tell you how to tell the difference by looking. Tires made for the USA market must bear the USDOT (UKMOT) mark and a lot of other info on them to show they comply with US rules. Along the sidewall of most tires sold in Europe you'll see the markings Treadwear......Traction......Temperature. Treadwear is followed by a three figure number and the others are followed by letters. The lower the Treadwear rating is, the softer the tire is, the more grip it should have and the faster it will wear out. I've seen numbers from about 170 to just over 700. You may get something like 100,000 miles of life out of a tire with the 700 index, but you would get sick of driving on it pretty fast as they are no fun. Somewhere around 300 is a good compromise between life and performance.
And yes, most tires sold in Europe will have the DOT mark and info on them. That includes tires like Uniroyal, that are not sold in the USA at all. When Uniroyal's original owners decided to sell the company, no one wanted to buy the entire operation. The European part went to Continental and the US part went to Michelin. Neither one can sell Uniroyal brand tires outside of their own territory. No European Uniroyals are sold in the US and no US Uniroyals are sold in Europe to avoid confusing things. So why does Uniroyal Europe put DOT markings on its tires that can't be sold in the land of the DOT? It shows that their tires are made to the highest standards anywhere as they also have the E-mark on them as well. Also, it lets Continental sell certain Uniroyal tires in the USA with the Conti name on them. The tires already passed all DOT requirements, so the rebadged version doesn't need to be tested again. The old Uniroyal RTT-2 was discontinued here when the Rainsport 1 came out. Instead of being retired, it became the Conti Extreme Contact in the USA and became quite popular.
And if you haven't guessed by now, I used to sell tires... Cooper (sold in the UK, they also own Avon) is the one to have if you want one that has a very long life and don't care about performance. Most mainline European tires are also good, but I prefer Conti and Uni with the original Premium Contact being my first choice.
