When the rout in prices ends for the world's iron-ore producers, those left standing probably will have more robots on their side.

Automated drills and driverless trucks are among the new tools employed by the four biggest companies, including BHP Billiton Ltd., in a bid to preserve profit margins during a bear market that began more than two years ago. Using more technology helped reduce costs at Rio Tinto Plc by eight per cent since 2013, even as it boosted output by five per cent, according to Paul Young, an analyst at Deutsche Bank AG in Sydney.

Improvements by top producers is defying a productivity collapse for the rest of the mining industry, which consultant McKinsey Co. says declined as much as 28 per cent in the past decade, forcing smaller operators to shut. With demand for ironore slowing in China, the world's biggest user, prices are probably headed lower as major suppliers expand output by tapping low-cost reserves, mostly in Australia, according to Citigroup Inc. The top four companies will see their share of the global market jump to 79 per cent in 2018 from 64 per cent in 2010, the bank said.

"Higher productivity is certainly an advantage" because those companies "would be the last ones to shut down in a low-price environment," said Jessica Fung, an analyst at BMO Capital Markets in Toronto.

The benchmark price of iron ore imported by China has plunged 69 per cent from a peak of US$191.70 a metric ton in February 2011 to US$59.01 on Thursday, heading for a third straight annual loss, according to Metal Bulletin. Iron-ore futures on the Dalian Commodity Exchange have dropped about 19 per cent this year.

Even with the decline, top producers remain profitable. The cash cost of mining the ore on average is US$15.80 a ton at Vale SA, US$16 for BHP, and US$16.20 at Rio Tinto, according to company data compiled by Bloomberg Intelligence.

With big companies still making money on iron ore, seaborne supply will exceed consumption by 58.1 million tons this year, and that surplus will peak at 107.4 million tons in 2018 persisting into 2020, Morgan Stanley said June 22. The push to get more efficient and use more automation is helping to drive the output gains, Citigroup said.

The race to increase market share as prices drop has already intensified competition among miners. Andrew Forrest, the founder of Fortescue Metals Group Ltd., said Aug. 24 that expanding output is causing "self-harm when industry leaders do it."

The persistent oversupply is "damaging the credibility of the industry," Glencore Plc chief executive officer Ivan Glasenberg said in May.

Smaller, higher-cost mines have been forced to scale back. Cliffs Natural Resources Inc., the largest U.S. producer, halted operations at Bloom Lake in northeastern Quebec in January. Other mines that were idled include Sinosteel Midwest Corp.'s Blue Hills in Australia and IMX Corp.'s Cairns Hill, Goldman Sachs said in a June 8 report.

"The companies that thrive will be those that are the most productive and efficient operators - and we are - and those who remain at the bottom of the cost curve - which we will," Rio Tinto CEO Sam Walsh said on an Aug. 6 earnings call. "Our highly sophisticated autonomous trucks demonstrate the value of our technology."

Operating costs across the mining industry, which had improved productivity in the lean years of the 1980s and 1990s, "got badly out of control" over the past decade as companies boosted output to satisfy booming demand, McKinsey said in May.