Now it’s time for L.A.’s three major oil companies to really start holding their breath.

Fresh on the heels of last week’s announced merger of Exxon Corp. and Mobil Corp., creating the world’s largest industrial concern, speculation here and on Wall Street has centered on further oil industry consolidation.

Share prices of Atlantic Richfield Co., Unocal Corp. and Occidental Petroleum Corp. remain depressed and would be easy pickings for a larger oil company that wanted to expand its presence on the West Coast and pick up substantial oil reserves.

“I’ve heard the rumors and, while we know nothing yet, we expect there will be more big announcements in the near future,” said Tom Burnett at Merger Insight in New York. “We expect to see something happen with Atlantic Richfield, Unocal, Chevron Corp. and Phillips Petroleum Co.”

As with other consolidations, the sheer fact that competitors are merging could make it imperative to find partners or acquirers to stay in the game. “Everyone is playing musical chairs,” said Burnett. “You don’t want to be the last one standing when the music stops.”

The need to merge will become increasingly pressing if oil prices remain near the current $11-per-barrel level, their lowest price in 12 years.

At this point, Arco remains at the center of most acquisition talk. The company’s stock was trading at around $66 a share as of late last week, down from near $80 as recently as July.

With heavy staff layoffs, the company is considered relatively lean. “Arco would make a very nice fit for someone who is crude-short and wants a greater presence west of the Rockies,” said Michael Smolenski, an independent oil analyst in Boston.

If Arco continues to report earnings as weak as those in the third quarter, when operating income fell 80 percent from a year earlier, it may be compelled to seek a partner, analysts said.

Arco would not comment on the takeover speculation other than to note that it has been downsizing to improve its competitiveness amid the industry consolidation.

Unocal and Occidental also are becoming likely targets, even though they both have a few warts that might make a potential acquirer think twice.

Over the years, Unocal has divested most of its downstream (refining and marketing) assets, and now is focused on oil exploration and production. While analysts have generally applauded that move, Unocal’s niche is under pressure due to soft demand for oil. That softness is being caused by the recession in Asia, predictions of a mild winter in the United States, and an unusually large amount of oil in reserve.

Unocal declined to comment on the takeover rumors. Spokesman Barry Lane did say the company continues to focus on oil exploration.

Occidental, meanwhile, has the double burden of being heavily invested in oil and chemicals. With most of the big oil companies having focused on oil, they may not want to invest outside their core business by acquiring Oxy’s chemical wing, analysts said.

Another weakness, analysts said, is Occidental’s recent Elk Hills acquisition. A year ago Occidental bought the oil and gas reserve near Bakersfield for $3.65 billion from the U.S. government. But oil prices have plummeted since then, and the view among industry experts is that Occidental overpaid on the deal.

Occidental executives did not return phone calls.

One factor that may slow down consolidation is the shrinking number of potential acquirers. In fact, for the Exxon-Mobil merger to avoid violating antitrust regulations, the combined company will likely have to sell off some of its West Coast refining operations. Texaco appears to be out of the market after its chairman, Bill Bijur, told analysts that he is not interest in a merger at this time.

One company that could be pressed to make an acquisition, or at least a partnership, is Chevron Corp.

In recent years, the San Francisco-based company has made major investments in developing oil fields near the Caspian Sea in Russia. While those fields are estimated to hold vast potential oil reserves, it could be years before they produce any profits. Meanwhile, the entire project could be disrupted by political tensions in that region.

In a move similar to Occidental’s purchase of Elk Hills, which was partially undertaken to offset risk from its Colombian operations, Chevron might be tempted to acquire something as stable as Arco’s Alaskan oil reserves. Such speculation has been further fueled by the fact that Chevron set up a mergers-and-acquisition unit earlier this year.

Chevron declined to comment on the speculation. “We are always looking for acquisitions that but we don’t get into what we are looking at,” said spokeswoman Dawn Soper.