Chad has ordered two major foreign oil firms, responsible for 60% of Chad's production, to quit the country in a row over taxes.
Chadian President Idriss Deby says the firms must go on Sunday
President Idriss Deby gave the order to US firm ChevronTexaco and Malaysia's Petronas.
"ChevronTexaco and Petronas must leave Chad because they have refused to pay their taxes," Mr Deby said.
However, Chevron says it has fully complied with tax demands and not had "official notification" to leave.
Meanwhile, Petronas could not be reached for comment.
The decision leaves only Exxon Mobil remaining in the consortium which handles the country's oil production.
President Deby said his government would take control of the remaining reserves.
The BBC's Stephanie Hancock in the capital, N'Djamena, says the surprise decision has sent shock waves around the oil industry.
The government has recently been hinting it wants to join the consortium, she says.
Privately, many observers feel the firms may have been kicked out to make room for Chinese oil companies. Just three weeks ago, Chad resumed diplomatic relations with Beijing.
If this proves to be true, it will mark a turning point for relations in this region, our correspondent says.
History of rows
Rows surrounding Chad's oil revenues have been simmering for months.
Earlier this year, Chad threatened to stop oil production if it did not immediately receive several months' worth of oil revenues from the US-led consortium.
And last December the government fell out with the World Bank, after it changed a law which controlled how oil revenues were spent.
The bank, which financially backs the oil project, repeatedly asked Chad not to change the law but it went ahead anyway.
In response, the bank froze all payments of oil revenues to the government.
That row was settled with a deal in July, under which Chad agreed to spend 70% of its oil revenues on development schemes, with 30% going into its overall budget.