BP has started the Thunder Horse South Expansion Project in the deepwater Gulf of Mexico, 11 months ahead of schedule.

Started $150m cheaper than expected, the project is anticipated to increase production at the facility by 50,000 gross barrels of oil equivalent per day.

BP chief executive Bob Dudley said: “Thunder Horse South Expansion, along with our recent approval of the $9bn Mad Dog Phase 2 platform, demonstrates that the US Gulf of Mexico remains a key part of our global portfolio today and for many years to come.

“This project also marks the first of several major upstream start-ups expected before the end of this year and a major step toward our goal of adding 800,000 barrels of new production by 2020.

“These new projects, coupled with a series of recent agreements we’ve reached around the world, reflect the growing momentum across BP and clear progress in building a strong foundation for the future.”

The expansion project will add a new subsea production system about two miles from the existing Thunder Horse platform.

This system offers a collection point for wells connected to the Thunder Horse platform by two 11,000ft flowlines that were installed on the seabed last year.

"The project is a major step toward our goal of adding 800,000 barrels of new production by 2020."

Around 15% of the project is completed below budget due to the utilisation of standard equipment and technology rather than building customised components.

The first new well for the project tapped into the hydrocarbon bearing sand at the Thunder Horse field and the drilling results indicated more than 500ft of net pay.

BP regional president of Gulf of Mexico business Richard Morrison said: “The Thunder Horse South Expansion project, brought online ahead of schedule and under budget, proves that deepwater can be done in a cost-effective way, while keeping a relentless focus on safety.

“It also shows the effectiveness of our strategy in the Gulf, which is all about increasing production from within our existing asset base and large portfolio of undeveloped resources.”

Developed jointly with ExxonMobil, the Thunder Horse platform is 6,000ft below water and originally began production in June 2008.

The platform has the capacity to handle 250,000 gross barrels of oil and 200 million gross cubic feet of natural gas a day.

In offshore Gulf of Mexico, BP operates four production platforms in Thunder Horse, Atlantis, Mad Dog and Na Kika. It also owns interest in Mars, Olympus, Ursa and Great White platforms.