Utilize the input text as a context reference, choose the right relationship between Petrobras and RIO DE JANEIRO from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

RIO DE JANEIRO Aug 28 Brazilian Senator Jose Serra said on Friday he expects a vote on changing the country's oil law to ease demands on state-run firm Petrobras and reduce local content rules to take place in September.

Answer: headquarters_location