06/13/2008 05:12 am ET | Updated May 25, 2011

Summer Airfares Double, Triple, Quadruple

The law of supply and demand is kicking in for airline passengers this summer -- and not in their favor.

Despite a string of price increases this year, demand for summer flights remains strong and the USA's big airlines are continuing to fill more than 80% of their seats.

This week, six (American, (AMR) United, (UAUA) Delta, (DAL) Northwest, (NWA) Continental, (CAL)US Airways (LCC)) raised prices again for flights on many domestic routes where there's no non-stop competition from low-fare carriers. The result, says travel price guru Tom Parsons of, is that the cheapest tickets available on many routes in July are 100% to 300% higher than a year ago.

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