Nearly all of an airline’s revenue comes from credit cards, particularly those focused on consumers, like Southwest Airlines.  Since Southwest is publicly traded, we can garner some interesting information about credit card processing rates from their financial statements. From P.24 of the Southwest Airlines 2007 10-K Annual Disclosure :

In absolute dollars, Other operating expenses increased $122 million, of which $39 million related to credit card processing fees. The $39 million increase in credit card processing fees represented a 22.2 percent increase from 2005 compared to the Company’s 20.2 percent increase in Passenger revenues. In excess of 97 percent of Passenger revenues are booked via customer credit cards, resulting in a close correlation between these two measures

Doing the math on this, we can find out how much they paid in 2006 in credit card processing fees ($39M / 22.2%) = $177.27M and how much they paid in 2007 ($177.27 * 122.2%) = $216.27M.  That’s enough to buy 54,000,000 gallons of jet fuel at current prices (around $4).

By the way, Southwest spent only $132M on its employees’ retirement plans (P.44).  Southwest also only made a profit of $645M in 2007, so in other words, the credit card issuers, processors and Visa and Mastercard made 1/4 as much from Southwest’s business as Southwest did.  Southwest also only paid $14M in dividends to shareholders, well less than the $216M that went to credit cards.

Southwest had $9,861M in revenue in 2007 (P.17), 97% of which was paid for with credit cards, so we can figure out the overall rate that Southwest is paying (  $216.72M / ($9,861M x 97%)) = 2.26%.