The oil equation for Mexico used to be simple: the higher the world price the better.

For example, the production cost of Haitian sugar was three times more than the world price in the 1980s.

The production cost of its uranium was three times the world price.

The fall in the world price of silver from 1872 on broke the 15 5 ratio.

They could out source everything to China and still charge 1st world prices.

The world price of oil has recently been around $18 a barrel.

The domestic price has historically set a floor on world prices.

"The world price has nothing to do with the cost of sugar," he said.

And why has the fall in world prices not been passed on?

At current production levels, every increase of a dollar in world prices means an extra $500 million a year.