UPDATE 1-BP's Atlantis oil platform starts up after delays

(Adds details)

LONDON, Dec 18 (Reuters) - BP Plc BP.L said oil and gas production had started at its 200,000 barrel-per-day Atlantis platform in the Gulf of Mexico, two years later than planned.

The London-based oil major said in a statement on Tuesday the facility would ramp up to plateau production, which should also include 180 million cubic feet of gas per day, over the next 12 months.

BP is looking to new projects such as Atlantis to turn around a nine-quarters run of falling oil and gas production.

However, long delays and cost overruns at Atlantis underline the challenges the company faces in addressing performance, which Chief Executive Tony Hayward described as “dreadful” in September.

BP is operator of Atlantis with a 56 percent stake, while Anglo-Australian miner BHP Billiton BHP.AXBLT.L has 44 percent.

BHP Billiton said its share of the cost to achieve plateau production at Atlantis was $1.63 billion, suggesting a total cost of $3.7 billion and more than $2 billion for BP.

BP said in 2002 that Atlantis production was scheduled to begin in 2005, and that BP’s share of development costs would “exceed $1 billion”. (Reporting by Tom Bergin; Editing by Mike Elliott and Quentin Bryar)