Three countries account for more than 60% of world phosphate rock production: the USA (31 %), Morocco (18%), & China (14%). However, Morocco, together with other producers in North Africa such as Tunisia, have the greatest influence on supply since the bulk of their output enters international trade. Expanding processing to downstream products at or near these phosphate rock mines has reduced rock trade in favor of processed phosphates like phosphoric acid, triple superphosphate, & the ammonium phosphates which have the advantage of high nutrient concentration (an increase in concentration from 30% to 40% results in a 25 % reduction in the transport and handling costs, an increase from 40% to 50% in concentration in a 20% reduction, and these costs can account for up to half the farm-delivered cost of a fertilizer).