The 2018 South Australian state election to elect members to the 54th Parliament of South Australia was held on 17 March 2018. All 47 seats in the House of Assembly or lower house, whose members were elected at the 2014 election, and 11 of 22 seats in the Legislative Council or upper house, last filled at the 2010 election, were contested. The record-16-year-incumbent Australian Labor Party (SA) government led by Premier Jay Weatherill was seeking a fifth four-year term, but was defeated by the opposition Liberal Party of Australia (SA), led by Opposition Leader Steven Marshall. Nick Xenophon's new SA Best party unsuccessfully sought to obtain the balance of power. Like federal elections, South Australia has compulsory voting, uses full-preference instant-runoff voting for single-member electorates in the lower house and optional preference single transferable voting in the proportionally represented upper house. The election was conducted by the Electoral Commission of South Australia (ECSA), an independent body answerable to Parliament. Results House of Assembly Seats changing hands Party-redistributed seats The seats of Colton, Elder, Mawson and Newland were won by Labor at the previous election, but the 2016 redistribution made them notionally Liberal seats. Colton, Elder and Newland were won by the Liberals; Mawson was retained by Labor. Legislative Council Aftermath Four hours after the close of polls, at approximately 10pm ACDT, incumbent Premier Jay Weatherill telephoned Steven Marshall and conceded defeat. Weatherill subsequently publicly announced that he had conceded, saying, "I'm sorry I couldn't bring home another victory, but I do feel like one of those horses that has won four Melbourne Cups and I think the handicap has caught up with us on this occasion." Marshall claimed victory saying, "A massive thank you to the people of South Australia who have put their trust, their faith in me and the Liberal team for a new dawn, a new dawn for South Australia!" After the SA Best party failed to win a seat including Hartley, Nick Xenophon ruled out a return to federal politics. Following the election outcome, Weatherill resigned as state Labor leader and returned to the backbench. Outgoing Minister for Health Peter Malinauskas became Leader of the Opposition, with outgoing Education Minister Susan Close as deputy, following a Labor caucus meeting on 9 April 2018. Notably, the Liberals won 16 of the 33 metropolitan seats, their best showing in the Adelaide area since their landslide victory in 1993,