MADRID (AFP) -- Foreign oil companies in Bolivia can expect to preserve "acceptable" margins of about 20 percent following the nationalization of the country's hydrocarbon assets, the Bolivian planning minister said Friday.

Under terms of a nationalization decree issued by President Evo Morales May 1 foreign companies have up to 180 days to renegotiate their contracts with the Bolivian national oil company YPFB.

During the transition period, 82 percent of profits earned by the companies -- as opposed to 50 percent at present -- will go to the Bolivian state and 18 percent to the corporations.

"The Bolivian government carried out a preliminary technical and economic study," Planning Minister Carlos Villegas told Spanish radio Cadena Ser.

"We were able to see that with 18 percent, companies would recover their investment and operational costs and achieve a margin of about 20 percent.

"I think that is rather acceptable if you compare this profit level with that enjoyed by the global oil sector."

Margins, whether expressed in net or gross terms, represent the difference between the price at which a product is sold and the operating costs of producing it.

Villegas justified the nationalization of the oil and gas sector by recalling that Bolivia, Latin America's poorest country, is faced with economic and social crises.

The May 1 decree affects 26 foreign companies, including such heavyweights as ExxonMobil of the United States, British Gas, Total of France and Repsol of Spain, and requires them to turn over to the Bolivian state company the ownership and exploitation of the country's energy resources.