Engineers found the leaks as they performed safety tests after last week's incident where an engine on an A380 exploded in mid air during a Singapore-Sydney flight, forcing the plane to perform an emergency landing.
"The oil leaks were beyond normal tolerances," Joyce told reporters. "So Rolls-Royce and our engineers have looked at what we have gathered as an accepted level and they have passed that threshold."
Qantas is grounding its fleet of A380s for a further 72 hours because of problems found in the tests.
"We are not going to take any risks whatsoever," Joyce said. "We want to make sure we have a 100 percent safe operation."