dml105, I don't believe it matters for upgrade purposes (and I ask other, more knowledgeable FT users to correct me if I'm wrong); it does matter for earning AAdvantage miles and LP (Loyalty Points) -- see https://www.aa.com/i18n/travel-info/...a-airlines.jsp for details. In general, AA-marketed flights earn based on fare, partner airline-marketed flights earn based on distance.