* Aena to sell licences for 26 airports
* Several firms have already shown interest
* Deadline for offers July 23
MADRID, July 2 (Reuters) - Spanish airport operator Aena has started the sale of licences to run duty-free shops at 26 sites, forecasting operators could see total annual sales of 700 million euros ($888 million).
Spanish and international companies have already shown interest and have until July 23 to make an offer, Aena said on Monday. The licences will start in 2013 and run to October 2020, save for some later start dates in the Canary Islands.
The shops, at sites including Madrid-Barajas - one of Europe's busiest airports, are currently run by Italian company Autogrill's World Duty Free Group (Aldeasa) and Swiss group Dufry.
Five firms, including The Nuance Group and Aelia, part of Lagardere, have shown interest, Aena sources said.
Duty-free shops in Spanish airports generated 535 million euros of sales for operators last year and 161 million euros for Aena, which ended 2011 with a loss of 220 million euros and 12 million euros debt. Aena expects to return to profit in 2014. ($1 = 0.7880 euro) (Reporting by Robert Hetz; Writing by Clare Kane; Editing by Dan Lalor)