Deep water covers 180 billion barrels of the world’s undiscovered oil and natural gas reserves, more than twice the amount yet found, Scottish energy consultants Wood Mackenzie said Wednesday.

Around two-thirds of oil and gas discoveries come from deep water now, as exploration successes on shore and in shallow waters become rarer, Wood Mackenzie said in a statement, citing a study it and fellow energy consultants Fugro Robertson conducted.

Brazil’s Petroleo Brasileiro (PBR), has reaped the most value from deep water drilling, with deep water assets worth around $27 billion, Wood Mackenzie analyst Andrew Latham told Dow Jones Newswires.

Latham said seas deeper than 400 meters are considered deep water.

U.K. oil giant BP PLC (BP.LN) comes in second, holding deepwater assets valued around $23 billion. Rival Royal Dutch/Shell is third, with assets worth $21 billion.

“To date, the geography of deep water has been the story of the ‘big four’ countries, Angola, Brazil, Nigeria and the U.S.,” Latham said, noting that Mexico looks set to join this group, once planned exploration by Petroleos Mexicanos SA (PEM.YY), or Pemex, begins.

Small and mid-size oil companies, such as Devon Energy (DVN), ConocoPhillips (COP), Kerr-McGee (KMG) and Murphy Oil Corp. (MUR) also have attractive exploration acreage, Wood Mackenzie said.

“In addition, Australia and Egypt have very substantial gas potential – each with yet-to-find potential of 80-120 thousand cubic feet,” Latham said.

However, market access for the gas in these countries appears limited in the near future, he added.

Despite the vast resources waiting beneath deep waters, exploitation is difficult, with technical troubles and political maneuvering in some countries causing project delays.

U.K. oil services company John Wood Group (WG.LN) warned just last week that deep water project delays would hit its earnings this year, though it expects a recovery in the market in 2005.

Wood Group said earlier this year that host governments in some deepwater provinces, such as West Africa, have put the brakes on some projects to boost the involvement of local companies. This, combined with a focus on short-term returns by some of the oil majors, has slowed deep water developments.