WASHINGTON (Reuters) - BP Plc installed a type of cement casing on its now-ruptured undersea well that it knew ran the risk of leaking gases in order to save money, The New York Times reported on Wednesday, citing a BP document it received from a congressional investigator.

Workers from the Deepwater Horizon oil rig and the energy company have said that gases were leaking through the casing hours before an explosion caused a massive oil spill in the Gulf of Mexico. Investigators have said the leaks could have caused the explosion.

The casing pipe that lined the well had cement that, if it did not seal properly, would allow gas to leak to the wellhead, where there was only a single barrier, the Times said.

Using a different type of casing would have created two barriers.

The newspaper said the company decided to use the casing several days before the explosion. It was installed by the contractor Halliburton.

BP said the riskier single barrier option made the best economic case, according to the newspaper.

On Wednesday, federal investigators said the cementing on the well must have failed at some point. Halliburton has defended its work, saying that all of its cementing procedures were dictated by BP.