Q+A - Who is running Israel?

JERUSALEM (Reuters) - Israel's parliamentary election looks likely to leave an inconclusive outcome when counting of votes cast on Tuesday is completed on Thursday, making it unclear who will succeed Prime Minister Ehud Olmert.

Here are answers to some key questions:

WHY WAS THE ELECTION HELD IN THE FIRST PLACE?

Israeli parliaments can last four years and the outgoing one could have kept sitting until 2010. But Prime Minister Ehud Olmert quit last year over a corruption scandal. He denies wrongdoing but police inquiries continue. Foreign Minister Tzipi Livni took over his centrist Kadima party in September. But she failed to build a majority in parliament, preferring an election over a deal with the religious Shas party, who wanted guarantees she would not give parts of Jerusalem to a Palestinian state and more welfare payments for its poor, ultra-Orthodox constituency.

LIVNI WON THE MOST SEATS, SHOULDN'T SHE BE PRIME MINISTER?

Not so fast. True, in Israel's 60-year history, the leader of the biggest parliamentary party has always been nominated prime minister, at least immediately after an election. But there is nothing in writing -- Israel has no formal constitution -- that obliges President Shimon Peres to ask Livni to forge a coalition. Benjamin Netanyahu, whose right-wing Likud party has a seat fewer than Kadima, says he is better placed to form a stable administration among the dozen or so parties who will sit in the Knesset. Livni has invited Netanyahu to join her team. Neither of their parties has even a quarter of the 120 seats.

SO WHEN WILL WE KNOW WHO IS PRIME MINISTER?

Peres is likely to take his time, consulting all parties, before nominating someone to try and form a government. Legally, he has a week from the publication of the official election results, something expected at present around February 18. He could use much of that time, analysts say. Peres is a former Labour prime minister who joined Kadima when it was founded in 2005 by former Likud premier Ariel Sharon. Whatever his own political preferences, however, the 85-year-old head of state's mandate is to nominate the person most favoured by members of parliament.

AND WILL PERES'S CHOICE THEN BE PRIME MINISTER?