Points will be awarded for original sleeping positions, the loudest snore and the most eye-catching outfits.
Spain's first national siesta championship is being held in Madrid.
Participants earn a maximum of 20,000 points for sleeping for the full 20 minutes.
The championship is intended to help revive the tradition of taking a nap after lunch.
What is billed as Spain's first national siesta championship is underway in Madrid to find the best napper and help revive the tradition of taking a snooze after lunch.
Participants are monitored as they lie on bright blue sofas in the middle of a shopping mall for a 20-minute nap. Some wear pajamas; others sport eye masks or cover their faces with their jackets.
They have pulse monitors attached to their bodies and the maximum of 20,000 points is awarded to those who manage to sleep for the full 20 minutes.
Sleeping fewer minutes means fewer points but judges also award marks for original sleeping positions, the loudest snore and the most eye-catching outfits.
The competition, organized by the National Association of Friends of the Siesta, began on October 14 and will wrap up on Saturday with the winner awarded a prize of 1,000 euros ($1,400).
"The mission of the championship is to spread the idea that the nap is something of ours that must be defended and practiced, because it is healthy and good for everyone," the association says on its website. "Being able to do it in public requires having a spirit of a champion and to be a great siesta taker."
Eight rounds of the competition are held daily with each involving five participants on sofas lined up in parallel lanes like those of a track and field meet.
"We were afraid that people would be afraid of making fools of themselves but on average about 50 people have taken part each day," the association's spokesman, Alvaro Vidal, told AFP.
Given the success of the siesta contest, the association is planning to repeat the event in the future and hold editions outside of Spain, he added.