Auto sales are down in Europe, but sales of Audi's A3 have been strong. The company rolled out this new sedan version to European buyers last month. Photo credit: Audi.

Last year, Volkswagen (NASDAQOTH:VLKAY) was the world's most profitable automaker, even though it was outsold by both General Motors (NYSE:GM) and Toyota (NYSE:TM). How'd that happen? Simple: Volkswagen has turned its luxury-car brand, Audi, into a huge source of profits.

Audi has continued to rack up big gains this year. As Fool contributor John Rosevear explains, Audi's recent sales gains have been surprisingly strong -- and those gains could mean big profits for VW in the coming quarter.

Fool contributor John Rosevear owns shares of General Motors. You can connect with him on Twitter at @jrosevearThe Motley Fool recommends General Motors. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.