* Brazil Bovespa falls 1.09 percent, Mexico IPC up 0.34 percent
SAO PAULO, Oct 29 (Reuters) - Brazilian stocks fell for the fourth session in five on Tuesday as investor concerns over a possible bankruptcy filing by heavily weighted oil firm OGX offset a jump in shares of lender Itau Unibanco.
Mexico's IPC index rallied for a third straight session, while Chile's bourse moved slightly lower.
Brazil's benchmark Bovespa stock index fell 1.09 percent a day after rising the most in nearly two weeks. Still, the index may finish October with its best monthly performance of the year.
Shares of troubled Brazilian oil producer OGX Petróleo e Gas Participações SA fell as much as 24 percent, contributing most to the index's decline after the company said talks with holders of $3.6 billion in its bonds ended without agreement. The company could file for bankruptcy protection as early as Tuesday, three sources with direct knowledge of the situation told Reuters on Monday.
The index was pressured further by shares of state-run rival Petroleo Brasileiro SA, known as Petrobras. Analysts said the 1.2 percent drop in the shares was driven mostly by profit-taking after the stock jumped the most in seven and a half months on Monday, fueled by news that the company would re-examine its pricing policy.
Shares of Itaú Unibanco Holding SA, Brazil's largest bank by market value, jumped 2.6 percent, reaching their highest in at least two years, after the company reported much higher-than-expected earnings for the third quarter.
Mexico's IPC index touched its highest level in over three weeks, adding 0.34 percent to 41,262.11.
Shares of broadcaster Grupo Televisa rose 0.95 percent, contributing most to the index's gains, while telecommunications firm America Movil, controlled by billionaire Carlos Slim, rose 0.3 percent.
Chemical maker Mexichem dropped 1 percent after the company reported a quarterly loss on Monday.
Chile's IPSA index edged 0.11 percent lower as a 1.3 percent decline in shares of pulp and paper company Empresas CMPC offset a 0.5 percent rise in retailer Falabella .