Amsoil, Signature Series oils - at the weights specified by Mazda, for a 2011 Speed3 and a 2010 CX-9 - have used Amsoil for many many years, going 15,000 miles between changes for the Speed3 and 20,000+ for the CX-9. As a dealer, they cost around $8.00 per quart, which is a small price to pay...