YAOUNDE (Reuters) - Cameroon's ruling party won 56 of the 70 seats contested in the country's first senate elections held on April 14, according to results issued on Monday by the Supreme Court.

President Paul Biya will appoint another 30 senators himself, ensuring his Cameroon People's Democratic Movement has tight control over the new 100-seat legislative body.

The creation of the senate is intended in part to clarify succession in the African oil producer nation, whose long-serving President Biya is now 80 years old.

The constitution says the head of the Senate would assume the interim in case of a mid-term presidential vacancy. It is unclear when a head of the senate will be appointed.

Security analysts have warned of chaos in central Africa's largest economy if Biya, who has kept an iron-fisted grip on power for more than 30 years, dies or retires before creating political space for possible successors.

Cameroon passed the law requiring the formation of a Senate 17 years ago but Biya's government delayed the polls, citing a lack of money. He announced the election date in February, without giving a reason for the timing.

Cameroon produced 22.37 million barrels of oil last year and expects output to rise in 2013 as new wells come online. The country is also the world's fifth-ranked grower of cocoa.

The main opposition party Social Democratic Front won 14 seats in the senate, according to the results, which showed voter participation at 98.27 percent amongst the nearly 10,000 municipal councilors who voted.

(Reporting by Tansa Musa; Editing by Richard Valdmanis and David Lewis)