Nigeria, a major oil producer, has been ranked the second most corrupt country in the world after Bangladesh, the BBC reported.
During a Berlin meeting of the global corruption watchdog, Transparency International, Obasanjo urged oil giants to open their books.
"Whatever you receive, you must publish," he said.
The BBC said Shell and BP have agreed to cooperate with the plan.
Although Nigeria is Africa's largest oil producer, most of its fuel is imported and most Nigerians live on less than $1 a day.
"The fight against corruption must be relentless and continuous," Obasanjo told a news conference. "The forces of corruption are determined."
He also appealed for international help in recovering funds stolen by former Nigerian rulers. The late Sani Abacha, for example, was suspected of having taken up to $3 billion out of the country.