Factbox: Spain has no easy options in search for a new government

All other parties fell or were stable and with no easy coalition in sight. Talks to reach a majority could take weeks. The constitution does not set a deadline for the process.

Following are the major issues and scenarios which will determine who becomes Spain's next premier:

CALENDAR

Once the new parliament and senate are operational, from July 19 onwards, it will be up to King Felipe VI to nominate a candidate to become prime minister though he would normally wait until the parties can agree on a nominee.

If the candidate fails to secure an absolute majority on the floor of the 350-seat lower house -- at least 176 votes -- then a second vote is held 48 hours later. At the second vote, the candidate only needs a simple majority of votes cast. With abstentions, the required majority would therefore be lower.

If the candidate still falls short, the King must put forward another one.

If no candidate can assemble a majority within two months of the first vote, new elections must be held.

Until December's inconclusive ballot, a parliamentary majority had always been secured within one to two months in all general elections held since 1977. If none is forthcoming this time, new elections may again be in the offing.

CENTRE-RIGHT PACT BETWEEN THE PP AND CIUDADANOS

A tie-up between the PP and the centrist Ciudadanos would reach 169 seats, just seven short of an absolute majority. They could potentially attract a further six seats from regional parties in the Basque Country and the Canary Islands.

In contrast to the last election, Ciudadanos leader Albert Rivera has not ruled out a pact with the PP, though the party has insisted that Rajoy should not lead any coalition.

'GRAND COALITION' BETWEEN THE PP AND THE SOCIALISTS

Rajoy's preferred option ahead of the vote was a "grand coalition" of the traditional conservative and socialist parties. This would total 222 seats and provide enough stability to keep reforming the economy over the next four years.

Socialist leader Pedro Sanchez had ruled out this option on several occasions before the election but on Sunday he said he would put the socialists' parliamentarians "at the service of the general interest".

PP MINORITY GOVERNMENT

If Rajoy were not able to secure the backing of centre-right parties or the Socialists, he could attempt to form a minority government with the PP's 137 seats. In that case, he would be relying on the Socialists and Ciudadanos to abstain in any test of confidence in his government.

CENTRE-LEFT COALITION BETWEEN UNIDOS PODEMOS AND PSOE

A combination of all left-wing forces would fall short of a majority with 156 seats and is highly unlikely given the falling support for the socialist party as well as major policy differences between Socialists and Unidos Podemos.

(Compiled by Dave Graham; Edited by Julien Toyer and Mark Bendeich)