The signing of the deal with BG E&P Brasil(BG Brasil) is the first step for the Thai company to expand its investment in South America, PTTEP chief executive Tevin Vongvanich said in a statement.
The four blocks -- BAR-M-215, BAR-M-217, BAR-M-252 and BAR-M-254 -- cover an area of about 3,077 square kilometres in the deep water of the northeastern Barreirinhas basin in the Atlantic Ocean.
BG Brasil is a subsidiary of the UK-based oil and gas producer BG Group. The deal is subject to approval from Brazil's National Agency of Petroleum, Natural Gas and Biofuels.
A PTTEP subsidiary will hold a 25% stake in the blocks, while BG Brasil, the operator, will hold 75%.
The joint-venture partners plan to start a seismic survey in the four blocks to assess their preliminary potential later this year, Mr Tevin said.
PTTEP, the flagship of majority state-owned PTT Plc and ranked among Asia's top 10 explorers, is scouting for oil and gas assets to expand energy security in Thailand, which relies on natural gas to generate almost 70% of its electricity.