BHP Billiton and Pemex have signed the paperwork on the Mexican state company's first-ever farm-out, a strategic partnership to develop the deep-water Trion field.

The Australian diversified mining company won the rights to partner with Pemex via a $624 million bid in Mexico's inaugural deep-water round last year.

The signing "constitutes a historic moment," according to Pemex chief executive Jose Antonio Gonzalez Anaya.

"For