* New targets could be reflected in next business plan * Petrobras production has fallen for past six months SAO PAULO, Jan 18 Brazil's ANP oil regulator asked state-led Petrobras to increase production at one of its largest fields, increasing costs for the firm that already has the world's largest corporate spending program, ANP board meeting minutes showed. Petrobras said in a statement published online on Friday that it has not been officially notified of the request from the ANP to make additional investments at its Roncador field. Roncador, one of Brazil's biggest producing fields in the Campos Basin, is among the older fields that have been responsible in the past six months for falling petroleum output from Petrobras, which provides for some 90 percent of Brazil's oil needs. As output falls at established fields, the oil giant has focused on developing more promising prospects in the so-called subsalt area along Brazil's coast near Rio de Janeiro, home to one of the world's largest oil finds in recent years. Petrobras may have to include revised production targets for Roncador in its next business plan mid-way through this year, two sources linked to ANP told Estado de Sao Paulo newspaper on Friday. The ANP will analyze development plans for 11 fields, including Roncador, that are run by Petrobras, according to the paper. Minutes from a Jan. 7 ANP board meeting showed the regulator approved a revised development plan for Roncador calling for new wells and platforms so that Petrobras can extract more oil from the field. The Estado de Sao Paulo newspaper estimated the investments could cost some 1 billion reais ($490,000). All oil firms operating in Brazil must have their projects approved by the regulator, which can ask them to adjust production targets. Petrobras has committed to spending $237 billion over five years to help meet its goal of more than doubling output to about 5.7 million barrels a day in 2020. Petrobras preferred shares, the company's most-traded class of stock, gained 0.41 percent to 19.8 reais.