Efforts to contain the Gulf of Mexico oil leak are finally showing signs of success, with operator BP announcing nearly half the oil spewing from a ruptured well is being captured.

BP says underwater robots have successfully inserted a tube into the well pipe, allowing oil to be pumped into a ship. About 2000 of the 5000 barrels pouring into the gulf each day are being recovered.

However, efforts to seal the leak have been unsuccessful. Scientists and US Government officials are also sceptical over the amount of oil leaking into the gulf, saying they believe BP is underestimating the size of the spill.

BP now estimates clean-up and containment costs will reach $US625 million ($750 million), nearly double the initial figure of $US350 million ($395.6 million).

The Insurance Information Institute estimates insured losses at $US1.4 billion ($1.54 billion).