"American companies will now have the certainty they need to invest confidently along our maritime border with Mexico," he said in a statement Wednesday.
A budget deal passed by U.S. lawmakers this week included consent for the Transboundary Hydrocarbon Agreement between the United States and Mexico.
The U.S. Interior Department estimates the transboundary region in the Gulf of Mexico holds as much as 172 million barrels of oil and 304 billion cubic feet of natural gas.
"The energy production made possible by this agreement will put Americans to work and raise more revenue for the government," Milito said.
API said as much as $51 billion in potential revenue could be generated from expanded work in the Gulf of Mexico.
The agreement follows a decision by Mexican legislatures to open up the country's oil sector to private investors, ending a 75-year state monopoly.