Leslie Manigat, also a former president, took about 13 percent and industrialist Charles Henri Baker seven percent, according to an official of the Haitian electoral council who asked not to be named.
The tabulation of the votes continued late on Thursday, two days after the presidential and legislative elections were held.
Tuesday's voting was the first since Haiti's last elected president, Jean Bertrand Aristide, resigned and fled the country on February 29, 2004.
Mr Preval, 63, who was president from 1996 to 2001, has distanced himself from Mr Aristide, with whom he used to have close ties, and in whose administration he served as prime minister in 1991.