Complex sentence: Alaska Airlines is not part of any of the three major airline alliances, but has codeshare agreements with airlines that are prominent members of Oneworld, such as British Airways and American Airlines, as well as prominent SkyTeam members like Air France and Delta Air Lines.
Split into simpler sentences: Alaska Airlines is not part of any of the three major airline alliances. However, it has codeshare agreements with some members of Oneworld, such as British Airways and American Airlines, and with some SkyTeam members, including Air France and Delta Air Lines.