(Adds Truss comments, detail on China, Malaysia contributions)
By Lincoln Feast
SYDNEY, Aug 6 (Reuters) - Dutch engineering firm Fugro will lead the search of the Indian Ocean seafloor where missing Malaysia Airlines Flight MH370 is believed to have crashed, hoping to unlock the greatest mystery in modern aviation.
Australia on Wednesday awarded Fugro the lead commercial contract for the search, after months of hunting by up to two dozen countries revealed no trace of the missing Boeing 777.
The jetliner, carrying 239 passengers and crew, disappeared on March 8 shortly after taking off from Kuala Lumpur bound for Beijing.
Investigators say what little evidence they have to work with suggests the aeroplane was deliberately diverted thousands of kilometres before eventually crashing into the Indian Ocean off the coast of Western Australia.
The next phase of the search is expected to start within a month and take up to a year, focusing on a 60,000 sq km (23,000 square miles) patch of ocean some 1,600 km (1,000 miles) west of Perth.
Australian Transport Minister and Deputy Prime Minister Warren Truss said Fugro was selected after "offering the best value-for-money technical solution" for the seafloor search.
"I remain cautiously optimistic that we will locate the missing aircraft within the priority search area," he told reporters in Canberra.
Fugro will use two vessels equipped with towed deep water vehicles carrying side scan sonar, multi beam echo sounders and video cameras to scour the seafloor, which is close to 5,000 m (16,400 ft) deep in places.
The Dutch company is already conducting a detailed underwater mapping of the search area, along with a Chinese naval vessel.
"We haven't completed the mapping, so we are still discovering detailed features that we had no knowledge of, underwater volcanoes and various other things," said Martin Dolan, the head of the Australian Transport Safety Board, which is heading the search.
"We are finding some surprises as we go through."
Malaysia will provide four vessels and gear to aid seafloor mapping and the search of the storm-lashed and isolated area.
Truss said he would talk to his Malaysian counterpart later this month about sharing search costs. Australia has set aside up to A$90 million ($83.66 million) and estimates a 12-month search of the area will cost around A$52 million.
The search is already the most expensive ever undertaken.
China, which had 153 nationals on board MH370, has been heavily involved, providing ships, aircraft and satellite technology. One Chinese vessel will stay in the search area until mid-September, but Truss said China had shown no sign that it would cover any of the commercial search costs.
Dozens of ships and planes scoured vast areas of ocean in the months after the plane disappeared but found only rubbish.
The search was narrowed in April after a series of acoustic pings thought to be from the plane's black box recorders were heard near its last location shown by satellite data analysis.
But officials now say wreckage from the aircraft was not in the area they had identified, requiring the search to be expanded and moved further to the southwest.
Malaysia Airlines has been battered this year by the tragic unprecedented loss of two of its airliners, after Flight MH17 was shot down over a conflict zone in eastern Ukraine.
With a long maritime history and seafaring expertise, Dutch companies are leaders in the field of complex, large-scale undersea search and salvage operations. (1 US dollar=1.0749 Australian dollar) (Additional reporting by Matt Siegel; Editing by Clarence Fernandez)