Supply Earlier this year, Goldman Sachs ( NYSE: GS ) said that total iron ore exports, by far Rio's most lucrative commodity, will surge from 1.15 billion tonnes this year to over 1.5 billion tonnes by 2015. This includes Australian capacity which is set to rise from 560 million tonnes to 780 million tonnes. Increases in supply from the world's biggest miners like Rio, BHP ( ASX: BHP ), Fortescue and Vale ( NYSE: VALE ) will account for only two-thirds of the increases until 2017, meaning more big mines will come online in the near future. It's a double-edged sword for Rio with both demand decreasing and supply increasing. Asset sales and debt Although Rio does not have the staggering levels of debt that Fortescue holds, it is still in need of capital to help its balance sheets.