A crippled Brazilian oil platform sank into the Atlantic Ocean off the coast of Rio de Janeiro and started spilling oil on Tuesday, five days after explosions on the giant rig killed 10 workers and damaged the finances and image of Brazil's state oil company. Despite efforts to save the P-36 platform, one of the world's largest, the 40-storey rig tipped and sank rapidly about 10.30am on Tuesday. Officials of Petrobras, the national company that still dominates Brazil's oil industry, said some of the almost 1.5 million litres of fuel aboard the structure had begun to leak.