A rebound in crude prices helped the world’s energy supermajors generate higher profits in the second quarter but ultimately it was how much oil and gas they produced that differentiated their fortunes.

For ExxonMobil, which was widely seen as having the worst performance of all the majors, higher prices were offset by a 7% drop in combined oil and gas production in the quarter from the same period last year.

Paul Sankey, an analyst from Mizuho in New York, described Exxon’s results as “shocking” and said the production number underlined the need for the world’s biggest energy producer to fast-track projects.

The company, once known for its focus on costs and returns, is spending heavily with capital expenditure increasing 68% from last year’s quarter. It is focusing on boosting output in the Permian Basin in the U.S. and new offshore discoveries in Guyana, but many projects are not expected to deliver oil output until the early 2020s.

Neil Chapman, senior vice president and a member of Exxon’s management committee, emphasized the company’s focus on “value” over “volume.” This has been the industry’s mantra over the past three years. But investors want to see output growth now.

“Few investors have got the patience these days to wait for five years or more,” Sankey added.

These concerns weighed heavily on Exxon’s share price, which has fallen to a lower level than when Brent crude last traded below $40 a barrel in March 2016.

For the wider Big Oil industry, production was not all bad news. Many are increasing output despite keeping costs in check. French major Total was an outperformer, adding almost 9% compared with the same quarter in 2017, taking output to record levels as investments it made in the downturn start to bear fruit.

However, Virendra Chauhan, analyst at Energy Aspects, said “free cash flow and liquids output trends were stagnant” across the sector.

Aware that securing new production is fundamental for future earnings, BP last week announced a $10.5 billion deal for BHP Billiton’s U.S. shale assets. Its biggest deal in 20 years will boost production, which was up by 1% in the second quarter.

“These assets will be vital in relation to BP’s efforts to maintain its overall production levels through 2025,” said Alisa Lukash, analyst at Rystad Energy, who added that the BHP deal would represent about 10% of BP’s total oil resources.

Christyan Malek, head of JPMorgan’s oil and gas research team in London, said as oil prices recover to more than $70 a barrel, companies—and investors—are starting to refocus on new barrels that underpin the entire business and shareholder returns.

“They are focusing more on volumes as a backstop to the cash flow targets they’ve set and the returns they’ve promised to investors,” said Malek.

Meanwhile, Royal Dutch Shell’s output declined by 2% but this was because of the sale of oil and gas fields.

Malek said that with the notable exception of Exxon Mobil, most energy majors had shown they were capable of growing output quickly even when investing less than it used to.

“We all thought production was going to fall off a cliff from Big Oil when they started slashing spending in 2014,” said Malek. “But it hasn’t. The majority of them are coming out on the front foot in terms of production.”

However, not all are convinced, with some industry observers saying that much of the production growth is coming from gas fields or shorter-cycle investment, such as U.S. shale fields, that ebbs and flows faster than large-scale developments of years past.

It is also not clear if this U.S. shale production can generate the same level of cash flows longer term. And if costs rise again, investment will have to pick up to maintain output.

Oil majors’ production also provides a guide to whether a collapse in investment after the 2014 price crash, particularly into traditional, long-term crude projects, is leading to an output crunch.

Paul Horsnell, analyst at Standard Chartered, said projects that were first approved in a world of $100 a barrel are coming online, but soon enough the massive capital expenditure pullback will kick in. “Declines are likely to pull ahead of output additions,” he said.

Ben van Beurden, CEO of Shell, said last week that greater investment into future production was necessary, but it would materialize only if there was confidence these investments “are going to pay up.”

For now, he said, shorter-term supply and demand fundamentals “point to a higher oil price,” and he hoped to “avoid a real supply crunch . . .[and] bring on enough new supply with a modest investment level.”