"Spain is a nation of sportsmen and sportswomen and our dream is to unite the world in 2012," he said.
"We Spaniards pursue values that unite people and make them better citizens. Spain is on good terms with our Mediterranean neighbours and all countries in the world.
"Above all, Spain is committed to peace, the environment and the fight against poverty."
London, Moscow, New York and Paris are also campaigning for the Games. They presented to the IOC earlier on Wednesday.
The decision, after a vote by all IOC members at the Raffles City Convention Centre, will be announced by president Jacques Rogge at around 1145 GMT.
Madrid's bid was illustrated by stylish video clips featuring flamenco dancing, Spanish beaches and city life over a soundtrack of rousing guitar music and sport.
"Our commitment to sport is absolute," Zapatero said. "We fight actively against doping and anything that casts a shadow over the Olympic movement."
Spanish IOC member Juan Antonio Samaranch Junior, whose father of the same name was IOC president when Barcelona staged the Olympics in 1992, promised a magical extravaganza.
The Spanish capital's mayor, Alberto Ruiz-Gallardon, went one step further. "We would deliver the best Games in history," he said.
Madrid's bid was given the royal stamp of approval when Spain's Queen Sofia said: "The whole of the Spanish royal family is convinced Madrid's plans would offer the world the best Olympic Games.
"I hope to welcome you all to Madrid."