SYDNEY (REUTERS) - Sanzaar will announce the future make-up of Super Rugby on Sunday, the governing body said on Saturday, bringing an end to a month of confusion and speculation about the format of the mostly southern hemisphere provincial competition.

Sanzaar, made up of the South African, New Zealand, Australian and Argentinian unions, met in London last month to hammer out a solution to the problems of an over-complicated structure.

The 18-team format, introduced in 2016 after Argentina's Jaguares and the Sunwolves of Japan joined the competition and South Africa's Kings returned, was widely criticised and there were fears the quality of the product was being diluted.

It seems certain that Australia and South Africa will lose one or more teams for 2018 to allow a return to the 15-team competition with the Western Force, Kings and Cheetahs franchises the most vulnerable.

The struggling Sunwolves, meanwhile, edged out South Africa's former champions Bulls 21-20 at Prince Chichibu Memorial Stadium in Tokyo on Saturday for their first win of the season.

Both teams scored two tries each and the result came down to kicking with Yu Tamura kicking a late penalty to earn the victory, reported the website superxv.com.

The Bulls had the opportunity to snatch victory but Francois Brummer missed a penalty kick three minutes from time, it added.