Odinga had 57 percent of the vote to 39 percent for Kibaki, The New York Times reported. About half the vote had been counted.

Voters also ousted many members of Kibaki's cabinet from their seats in parliament. Odinga won in the parliamentary district he has represented for 15 years. In Kenya, the president must also be a member of parliament.

"This vote is more anti-Kibaki than pro-opposition," Chweya Ludeki, a political scientist at the University of Nairobi, told the Times. "The president was seen as doing a bad job in terms of ethnic balance."

Odinga, leader of the Orange Democratic Movement, is a member of the Luo tribe, and voters expect him to be fairer than Kibaki, the newspaper said. Kibaki is a Kikuyu and thus a member of the tribe that has dominated Kenya since it won independence.

The son of a successful businessman, Odinga ran as a populist. His father, despite his wealth, was a socialist who sent Odina to East Germany for his education.