Brazil's Petróleo Brasileiro SA said on Tuesday it is in the last stages of talks to sell a minority stake in a natural gas distribution holding company to Japan's Mitsui & Co Ltd, in its drive to dispose of over $13 billion worth of non-essential assets by the end-2017.

In a securities filing, Petrobras said it is engaged in "final negotiations" with Mitsui's Mitsui Gas e Energia do Brasil Ltda over the sale of a 49 per cent stake in an investment holding company comprising the interests that Petrobras has in regional gas distributors across Brazil.

Petrobras did not give an estimate of the value of the transaction, which hinges on management, board and regulatory approval. The stake sale in the holding company forms part of an asset divestment plan that Petrobras already announced for the 2015-2019 period.

By partially divesting assets in gas and fuel distribution, biofuels and transport equipment, Petrobras chief executive officer Aldemir Bendine is aiming to speed up the development of promising offshore oil discoveries known as subsalt. Still, Petrobras - the world's most indebted major oil company - is putting those assets on the block at a time of plunging oil prices and limited interest from potential buyers.

The gas unit stake sale gained traction as Petrobras put off the spin-off and a subsequent initial public offering of the BR Distribuidora SA fuel distribution unit, according to analysts including Banco Brasil Plural's Caio Carvalhal. He estimates the unit to be worth up to $3 billion.

Some of them say that Mitsui has long been seen as a natural buyer for some of Petrobras' non-core assets because of its knowledge of Brazil and its ability to remaining as a minority shareholder in large projects and businesses in the country.

Mitsui is "already a Petrobras partner in eight gas distribution companies in Brazil, and could leverage on potential operational synergies," Carvalhal said.

Common shares of Rio de Janeiro-based Petrobras shed 2 per cent to 8.46 reais on Tuesday. The stock is down 11 per cent this year.- Reuters