Short of a technological breakthrough, the vaunted Monterey Shale oil formation underlying much of the southern Central Valley will yield no more than about 600 million barrels, or 96 percent less than previously believed, according to the U.S. Energy Information Administration.

The lower estimate, reported Wednesday by the Los Angeles Times, could be a big disappointment to Kern County's oil industry, which in recent years has attracted large investments from companies anxious to tap what the EIA had said was nearly 14 billion barrels of California shale oil.

The biggest single investor, Los Angeles-based Occidental Petroleum Corp., declined to comment, instead referring questions to the trade group Western States Petroleum Association.

WSPA spokesman Tupper Hull said techniques will eventually open up the Monterey.

"We have a lot of confidence in the intelligence and skill of our engineers and geologists to find ways to adapt," Hull told The Times. "As the technologies change, the production rates could also change dramatically."

The EIA's earlier estimate of the Monterey's potential has not only lured large national companies to Kern County, but it has prompted warnings from politicians including Rep. Kevin McCarthy, R-Bakersfield, that new regulation of hydraulic fracturing -- the controversial but effective oil field technique known as "fracking" -- could hamstring the state's Monterey oil-fueled economic boom.

University of Southern California researchers projected last year that developing the Monterey would add nearly 3 million jobs and close to $25 billion in tax revenues by 2020. Some of their conclusions were based on the shale energy boom under way in North Dakota and other states.

But local oil executives have expressed doubts about the deep and geologically diverse "source rock" thought to be the largest deposit of its kind in the country. Joined in their skepticism by Wall Street analysts and other industry observers, executives including Aera Energy LLC President and CEO Gaurdie Banister have said over the past year that it could be at least several years before local geologists and engineers figure out how to efficiently tap the Monterey.

They say the problem is that California's seismic history has made its geology far more complex than that of the prolific Bakken Shale in and around North Dakota. Geologists say Monterey Shale oil wells tend to produce well at first but then their flow tapers off sharply.