In a statement, the PDP governors and governorship candidates said:
"After due consideration of all the aspirants on the platform of the party, we have resolved to support the candidacy of Umaru Yar'Adua."
Yar'Adua, who suffers from a chronic kidney condition, is the president's favourite.
Party sources said many contestants withdrew from the race on Friday but Aliyu Gusau, former national security adviser to Obasanjo, was still determined to force a vote at Saturday's convention.
One senior delegate said: "Gusau is the most formidable challenger, but Yar'Adua certainly looks like the favourite."
With deep pockets, tight control over security forces and an unrivalled nationwide network, the PDP is the party to beat in April's landmark vote which should mark the first handover from one elected president to another in Africa's biggest oil-producing country.
|Obasanjo, the Nigeria president, cannot stand again|
Analysts say the opposition is gaining strength with people growing disaffected with the PDP.
Obasanjo, who must step down next year after failing to amend the constitution and stay in power, has tightened his grip over party structures in the past few months.
The retired general has imposed candidates at the local and state levels, causing widespread disaffection among the losers. Critics accuse him of using the government's anti-corruption squad to intimidate opponents.
Return to democracy
Obasanjo's election in 1999 marked a return to democracy after three decades of almost continuous army rule. But bribery, violence and rigging are still the currency of politics.
The opposition aims to capitalise on splits in the PDP and lack of support for Yar'Adua.
Two main opposition parties, All Nigeria People's Party (ANPP) and Action Congress (AC), signed an alliance this week that analysts expect to lead to former military ruler, Muhammadu Buhari, becoming their candidate.
They hold their presidential primaries on Sunday and Monday respectively.