I guess it depends how you measure size. If you select number of passengers, then Southwest just surpassed American; however, the new Delta is now bigger than LUV. CO is about seventh or eighth. If you base the assessment on equipment or fleet size, which I think is also pretty reasonable, then CO is number six (DL is the largest, then AA followed by Air France/KLM then WN). CAL is certainly the fifth largest in the US; if you look at Air France and KLM as two separate entities, then CAL becomes number five.