The central leadership decided to convene separate meetings of the PPP's parliamentary party and the members of the ruling coalition to choose a leader to replace Gilani, the sources said.
Federal ministers Chaudhry Ahmed Mukhtar, Makhdoom Shahabuddin and Khursheed Shah are among those being considered for the post of premier, the sources added.
A session of the National Assembly or lower house of Parliament is likely to be convened tomorrow for the formal election of the new premier.
A three-judge bench headed by chief justice Iftikhar Chaudhry issued the ruling disqualifying Gilani in response to several petitions that had challenged National Assembly Speaker Fehmida Mirza's decision not to disqualify the premier following his conviction of contempt nearly two months ago.
The bench ruled that the post of premier had been vacant since April 26, when another seven-judge bench had convicted Gilani of contempt for refusing to reopen graft cases in Switzerland against President Zardari.
The bench directed the Election Commission to issue a notification stating that Gilani was no longer a member of parliament.
The judiciary and the government have been locked in a standoff since December 2009, when the apex court struck down a graft amnesty issued by former military ruler Pervez Musharraf that benefited Zardari and over 8,000 others.