If you're looking to go on holiday using frequent-flyer miles this summer, doing so on Southwest's Rapid Rewards program is your best bet - almost 99.3 percent of seats are available for reward point bookings, according to a survey released May 3.

Consulting company IdeaWorks and travel booker ezRez made some 6,100 queries to 22 loyalty programs around the world in February and March, requesting their frequent flyer seat availability between June and October 2010.

They found that Southwest had the highest availability of any airline they queried. Air Berlin's topbonus program came in second place, with 98.6 percent availability, while Air Canada came third with 93.6 percent.

At the bottom of the list was US Airways, for which only 10.7 percent of queries returned outbound and return reward seats. Delta came second to last, with 12.9 percent availability.

Unfortunately for consumers, it seems that the value of airline loyalty points for travel is very much down to which program you're a member of.

Ideaworks warns that airlines now have a multitude of ways to allow customers to spend their miles, and that the airlines at the top of its list made a conscious decision to value frequent flyers over the revenue brought in by selling seats to cash-paying customers.

"More airlines are choosing to solve reward availability issues by allowing members to redeem miles, kilometers, credits, and points for hotel accommodations, car rentals, personal services, and merchandise," explains John Swanciger, from ezRez Software.

"These methods provide more opportunities for members to spend frequent flyer currency."

Overall Reward Availability

Ranked High to Low - Seat Availability for June - October 2010

99.3% Southwest (Rapid Rewards)
98.6% Air Berlin (topbonus)
93.6% Air Canada (Aeroplan)
90.0% Virgin Blue (Velocity)
85.7% Lufthansa/SWISS/Austrian (Miles & More)
77.1% Singapore Airlines (KrisFlyer)
76.4% Iberia (Iberia Plus)
75.0% Alaska Airlines (Mileage Plan)
72.9% Jet Airways (Jet Privilege)
72.9% Qantas Airways (Frequent Flyer)
71.4% Continental Airlines (OnePass)
68.6% United Airlines (Mileage Plus)
67.9% AirTran Airways (A+ Rewards)
67.1% Cathay Pacific (Asia Miles)
65.0% British Airways (Executive Club)
64.3% SAS Scandinavian (EuroBonus)
57.9% American Airlines (AAdvantage)
56.4% Air France/KLM (Flying Blue)
36.4% Emirates (Skywards)
35.3% Turkish Airlines (Miles&Smiles)
12.9% Delta Air Lines (SkyMiles)
10.7% US Airways (Dividend Miles)

Data from IdeaWorks Company http://www.ideaworkscompany.com /