MONTEVIDEO, Uruguay (AP) — Uruguay has inaugurated a desulfurization plant for the county's sole oil refinery.

The refinery expansion in Montevideo is a joint venture of Argentina's state-owned YPF and Uruguay's ANCAP oil companies.

The plant will reduce by 99.5 percent the amount of sulfur in diesel fuel and some 85 percent in gasoline to improve ANCAP's environmental standards and efficiency. The sulfur will be collected and sold to a Uruguayan company to be used for fertilizers.

Argentine President Cristina Fernandez said during the plant's unveiling Tuesday that the $400 million investment marks a milestone in relations between the neighboring nations.

Uruguayan President Jose Mujica said the expansion helps ANCAP to remain in the industry as the sulfur was badly damaging the refinery's equipment. Uruguay's presidency puts the investment at about $350 million.