Petrobras and Russia's Rosneft and HRT sing dealBRASILIA, Aug 14 (Reuters) - Russian state oil company Rosneft signed an agreement with Petrobras to seek ways to sell natural gas available in remote regions of the Amazon jungle, the companies said on Monday. The companies did not give details of the agreement, and simply saying that is a "letter of intent". Rosneft holds a 51% stake in oil and gas blocks in the Solimões Basin, west of Manaus, Amazonas, in partnership with HRT, which owns the other 49%. The blocks contain reserves estimated at 542 million barrels of oil equivalent, with 83% of this volume is contingent natural gas, according to HRT. The contingent reserves are comprised of oil and gas that have been discovered, but not all have factors that ensure its commercial viability. The currently estimated reserves are equivalent to the amount of oil the United States uses in a month. The agreement between Rosneft and Petrobras was signed during a visit by Russian President Vladimir Putin to Brazil. Two years ago, HRT and Petrobras signed a memorandum of understanding to study options for gas sales on Amazon. Despite the agreement and numerous studies, no solution has been found. Explore Gas in the Amazon is difficult due to the distance to major consumer centers and complexity of the construction of pipelines in the jungle. Within the region of Manaus and gas, consumer center closest, about 900 km of dense forest. The nearest pipeline, Petrobras, was built for the Brazilian state can drain your own gas produced in the region. "We have different options ... need to sell gas and Petrobras has a transportation system to which they could have access, and we will discuss these issues," he told reporters the president of Rosneft, Igor Sechin during Putin's visit in Brazil. (By Alexei Anishchuk and Silvio Cascione)