United and its Star Alliance partners like Air Canada have declared a fare war on Delta, offering flights to Europe out of Delta hubs for as little as $312 roundtrip.

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You can fly from cities like Atlanta, Detroit, Minneapolis, and Salt Lake City to places like Rome, Amsterdam, Paris and Milan for less than $350. (HT: Fly 4 Free) Other cities in Italy are available for about $50 more as well.

Fares on most sites will run about $50 more, still a great deal, but these lowest fares can be found using airfare metasearch site Momondo.

A year ago I highlighted excitement over roundtrip fares to Amsterdam for under $600 roundtrip. Several cities were available in the $700s. I wouldn’t even bother posting about those fares today.

Low fuel prices have led to more aggressive airline competition. Fear and economic uncertainty have dampened European travel, so there are more empty seats for airlines to sell at a deep discount. And we have transatlantic low cost carriers now too. So we’re regularly now seeing fares that were unthinkable a year or two ago. But here’s why we see the best deals as flash sales rather than lower regular prices.

If choosing actual United flights for your trip you can credit the miles for these trips to Singapore Airlines KrisFlyer and earn more than you would any other way.

While a non-elite MileagePlus member crediting United flights to the revenue-based MileagePlus program will only earn 5 miles per dollar on the cost of the ticket excluding taxes, nearly all United fares earn 100% of flown miles when crediting to Singapore Airlines KrisFlyer (.pdf). That means you earn 5-10 times as many miles with Singapore Airlines KrisFlyer for your trip flying United than you would crediting to MileagePlus.

While Singapore miles do expire after 3 years (not 3 years of inactivity), you can top off a KrisFlyer miles account with transfers from American Express, Chase, Citi, and Starwood.