Seven major oil and gas companies could increase their collective value by roughly $100 billion if they bring their future investments in oil and gas fields in line with plans to limit global warming to 2 degrees Celsius, according to a new assessment.

Investors "may be surprised at just how much value can be created by oil and gas companies in a carbon-constrained scenario," said the report, published Wednesday by the Carbon Tracker Initiative, a think tank based in London.

At current oil prices, the group estimated that the portfolio of the combined majors' oil and gas projects would be worth about $140 billion more if they left enough fuels in the ground to keep the world within the carbon budget for 2 degrees. Even if oil prices rebounded to $100 per barrel, sticking to the 2-degree target would produce $55 billion higher valuations than a business-as-usual approach.

"You can actually create more value for your shareholders by investing as if preparing for a low-demand world," said Andrew Grant, a financial analyst with Carbon Tracker.

The study comes at a time when shareholders and financial regulators are challenging energy companies to fully explain and disclose the risks they face as the world turns away from fossil fuels in order to head off dangerous climate change.

The study looked at oil and gas asset investments by the world's seven largest privately owned oil and gas companies, including oil giants ExxonMobil, Shell and BP. An approach that pursues significant investment in finding and drilling new, costly fields only makes financial sense when oil prices exceed $120 per barrel for a sustained period, the report found. Long-term forecasts from the Organization of Petroleum Exporting Countries and the International Energy Agency predict oil will remain below $100 per barrel until 2040.

"By investing less you actually end up with more," said Andrew Logan, director of the oil, gas and insurance programs at Ceres, a Boston-based non-profit that works with the business community on sustainability and climate change issues. "It's counterintuitive, but the business-as-usual approach effectively destroys capital. You can end up with less than you started."

To maximize returns, oil and gas companies should eliminate future investments in high-cost projects, such as Canada's tar sands or deep undersea reserves, the report stated.

"Companies will need to be a bit more disciplined on which projects they sanction and which ones they don't," Grant said. "It's about focusing on the lower-cost, high-margin projects that deliver a greater result for your shareholders at lower risk."

Earlier studies by Carbon Tracker and others have looked at "stranded assets," or unburnable carbon, the oil or gas reserves that would have to stay in the ground if governments move to limit global warming to 2 degrees, the target at the heart of the Paris Agreement on climate change. The current study takes the concept further.

"They've really run the numbers and shown there is a tangible economic case for actually investing less in higher cost projects," Logan said. "What is new is this move from the somewhat theoretical level that assets could be stranded to a more tangible approach that shows where to invest and where not to invest."

"Now the conversation becomes a more focused one of how do you evaluate companies and business strategies in light of carbon asset risk," Logan said. "This report helps jumpstart that conversation."

How the oil and gas industry would spend money that it doesn't invest in acquiring high-cost assets, however, remains unclear.

"Does it use that capital to finance some sort of slow transition away from fossil fuels as their core business, or does it return that money to investors and just engage in a very long and profitable going-out-of-business sale?" Logan asked. "Industry hasn't figured that out."

Graphic explanation, via Carbon Tracker: