According to an unnamed source, BP PLC was on the verge of announcing a significant oil discovery in the Gulf of Mexico when tragedy struck a drilling rig this week.

A person familiar with the situation told it the oil producer was days away from making the "commercially attractive" find public, The Wall Street Journal reported on Thursday.

The business newspaper has reported that the source said that the Macondo prospect, where the rig was drilling, contained "tens of millions of barrels" of oil reserves.

But then on Tuesday an explosion hit the Deepwater Horizon rig, which BP had leased from the operator, Transocean Ltd. of Switzerland, leaving 11 workers missing. It sank Thursday.

The Journal further said that experts say the rig, which had been reaching through 5,000 feet of water to a total depth of 8,350 feet, likely was done in by an uncontrolled release of fluids called a blowout.

It will cost more than $600 million to replace, analysts have said.

If the Macondo field is ever developed, it would not have its own production platform, the Journal's source said.

The newspaper further said that instead, it would be connected to an existing one at BP's nearby Pompano field. (With Inputs from Agencies)