(Reuters) – Oil major Chevron Corp’s $33 billion deal on Friday to acquire Anadarko Petroleum Corp has some investors and industry executives asking whether it is time for other U.S. shale oil and gas producers to consider selling themselves.

Anadarko has been one of the pioneers of the shale revolution, which turned the United States into the world’s biggest oil producer, overtaking Russia and Saudi Arabia. The Houston-based company’s willingness to ink a sale, rather than capitalise on oil prices rebounding, illustrates the significant challenges facing many U.S. shale producers.

These challenges include exploration and production becoming more expensive, as the oil and gas that is easier to access gets scarcer and existing wells turn less productive. Deep-pocketed oil majors such as Chevron can better cope with these costs, because they can get cheaper drilling rates by committing to longer contacts and afford cutting-edge technology to get more out of wells.

Shale producers such as Pioneer Natural Resources, Continental Resources, Diamondback Energy and Concho Resources have already been under pressure from investors to improve their profitability. Many investors now say Chevron’s deal will embolden them to grill companies in the sector whether it is time to throw in the towel and sell.

“If you have large acreage positions like Pioneer and Concho, or lesser but more contiguous positions like Parsley Energy, and you’re a pure-play Permian producer, there’s no doubt that you are on the radar screen for these majors,” said Rob Thummel, portfolio manager at Tortoise Capital Advisors.

Pioneer, Concho and Parsley shares rose 11.5 percent, 8.8 percent and 11.7 percent respectively on Friday following the announcement of the sale of Anadarko, amid investor speculation over who the next takeover target will be.

U.S. financial services firm Cowen & Co said independent producers expect to spend about 11 percent less in 2019, while major oil companies plan to spend about 16 percent more.

Pioneer, one of the Permian’s largest producers, said in February it plans to reduce 2019 capital expenditures by 11 percent, or about $350 million, in an effort to appease investors.

While there has been dealmaking in the last 12 months – both Concho Resources Inc and Diamondback Energy Inc have bought rivals – many of the large producers which spent years gobbling each other up have been sitting on their hands, under shareholder pressure to focus on creating stronger returns.

The sale of Anadarko could likely change that for potential acquirers, including ConocoPhillips and Occidental Petroleum Corp, the two largest U.S. independents behind the majors. Occidental was the rival bidder that lost out to Chevron in the race to buy Anadarko, sources said on Friday.

“At some point in time in the next few years the majors may reach out,” Pioneer CEO Scott Sheffield told Reuters this week, before Chevron’s acquisition was announced.

He declined to comment on whether majors had approached Pioneer directly.

Asked about his appetite for deals in February, Conoco CEO Ryan Lance said it would have to be an unusual opportunity for the company to consider an acquisition.

“We are not feeling any pressure to do anything,” he said.

RUNNING OUT OF INVENTORY

Given the substantial production forecasts being offered by some of the majors such as Exxon Mobil Corp, they will need to acquire new acreage at a big scale to offset the often sharp declines experienced by shale wells.

The majors “are eventually going to run out of inventory,” said Pioneer’s Sheffield. “They are drilling their inventory faster than the independents, so they are going to run out a lot faster, in my opinion.”

BP Plc and Royal Dutch Shell Plc, which lag peers like Exxon and Chevron in the Permian, could make acquisitions to gain more exposure to the formation, analysts said.

Shell was seen as the leading contender to buy privately owned Permian producer Endeavor Energy, people familiar with the transaction told Reuters, but the two companies have, so far, failed to agree on Endeavor’s valuation.

Shell is further constrained by its target to spend only $30 billion on capital projects in 2019, including acquisitions, said Noah Barnett, an analyst at Janus Henderson.