Not all oil weighs equally on the scales of climate change.

New research from Stanford University finds that in 2015, nearly 9,000 oilfields in 90 countries produced greenhouse gases equivalent to 1.7 gigatons of carbon dioxide – roughly 5 percent of all emissions from fuel combustion that year. On average, oil production emitted of 10.3 grams of emissions for every megajoule of crude, but nations with the most carbon-intensive practices cranked out emissions at nearly twice that rate.

offshore oil platform

New research quantifies greenhouse gas emissions from crude oil production – from when companies first explore a site through transporting crude to refineries. (Image credit: Getty Images)

The research, published Aug. 30 in the journal Science, quantifies emissions from when companies first explore a site through transporting crude to refineries. Accounting for as much as 98 percent of global production, it is the most comprehensive assessment to date of carbon intensity and pollution by oil fields.

Yet according to lead author Mohammad Masnadi, a postdoctoral researcher at Stanford University’s School of Earth, Energy & Environmental Sciences (Stanford Earth), total emissions from crude oil production may be higher than even these latest calculations suggest, because the current analysis does not fully capture emissions related to leakage and venting of methane, a powerful global warming gas. Masnadi worked with Adam Brandt, an assistant professor of energy resources engineering and senior author on the paper.

The work suggests nations with the highest carbon-intensity produce more than 15 grams of carbon dioxide equivalent, on average, for every megajoule of crude. That’s roughly triple the average carbon intensity of oilfields in countries at the low end of the scale.

Wasted gas

Nothing drives up carbon intensity like the practice of routinely burning, or flaring, natural gas, the researchers found. “Everybody talks about heavy crude oil, oil sands and unconventional resources,” Masnadi said. But the research shows that a country like Algeria, which produces the lightest crude oil in the world, has the highest carbon intensity because oilfield operators routinely burn large amounts of gas. Saudi Arabia, meanwhile, has relatively low carbon intensity because it flares little gas and has vast resources with low water content, which means less energy goes into treating and separating the oil.

The revelation suggests that investment in infrastructure and policies to better manage natural gas could deliver greater climate benefits than previously thought. “Really, the challenge with flaring is there needs to be a policy or a regulatory apparatus to say, ‘Burning gas with no purpose isn’t allowed; put it back in the ground or find something useful to do with it,’” Brandt said.

To be sure, emissions related to a reservoir’s location and accessibility still play an important role. The paper finds Venezuela and Canada rank among the most carbon-intensive oil producers because of the high energy needs and emissions associated with extracting heavy oil from unconventional reserves like tar sands. And so-called enhanced recovery techniques that use steam to loosen oil from aging wells add to the relatively high carbon intensity of oil production in places like Indonesia, Oman and California.

In all, the study suggests that eliminating routine flaring and cutting methane leaks and venting to rates already achieved in Norway could cut as much as 700 megatons of emissions from the oil sector’s annual carbon footprint – a reduction of roughly 43 percent. And over the coming century, the world could avoid as much as 18 gigatons of emissions from the oil production expected to continue under even aggressive scenarios for shifting away from fossil fuels – mainly by halting extraction of the dirtiest resources and improving gas management.

Estimating emissions

The study builds on a project led by Brandt called the Oil Production Greenhouse Gas Emissions Estimator, or OPGEE, which California air regulators now use to estimate emissions from different crudes that California imports or produces as part of the state’s low-carbon fuel standard.

But until now, large gaps remained in even the best estimates of emissions from crude oil production on a global scale because they worked backward from economic data, calculating how many barrels oil companies were likely to have produced based on oil prices in a given period. According to Masnadi, “When you do this, you’re missing lots of underlying processes that lead to emissions.”

The new simulator, by contrast, calculates emissions from the bottom up. The researchers developed models of the physical processes involved at each stage from initial exploration through transport to refineries. Data-intensive calculations for a single field could require measures for up to 50 parameters, including oil density, production rates and the amount of natural gas that the operator burned or captured in pipelines – as well as whether a producer injects water or steam to coax crude from wells, or uses some other method.

Gathering that kind of detail for thousands of active oil fields around the world was daunting. “It’s the first time we’ve been able to do this at this very resolved oil field-by-oil field level,” Brandt said. But as few as 1,000 fields account for nearly two-thirds of global production, and the researchers realized they could focus on mining open-source data sets for those heavy hitters. For the remaining fields – mostly smaller scale producers – they could find information in private databases.

The group ultimately scoured public sources, including peer-reviewed research, news reports, technical reports, government databases and literature from the Society of Petroleum Engineering for one year, and then partnered with companies to gain access to two proprietary data sets. They then assigned quality scores to the different data sets, giving more weight to peer-reviewed sources and less to news reports and commercial sources that they agreed to keep private.

Societies remain heavily dependent on crude oil, which today goes into products ranging from asphalt and jet fuel to fertilizer and medicine. “Everybody lives based on these fossil fuel resources,” Masnadi said. “It’s not very feasible to get rid of this energy resource in one night or in one year.” The question is how to accelerate that transition. Part of the answer provided by this paper is understanding in fine detail where we stand today – and why. “Now we can move forward.”

Adam Brandt is also a center fellow, by courtesy, at the Precourt Institute for Energy. Additional co-authors are from Aramco Services Co., Ford Motor Co., University of Calgary, Carnegie Endowment for International Peace, Carnegie Mellon University, University of British Columbia, California Environmental Protection Agency, National Renewable Energy Laboratory, University of Michigan, International Energy Agency, Baker Hughes, Chalmers University of Technology, Cornell University and Argonne National Laboratory.

The work was funded by the Natural Sciences and Engineering Research Council of Canada, Aramco Services Co., Ford Motor Co., the Carnegie Endowment for International Peace, the Hewlett Foundation, the ClimateWorks Foundation and the Alfred P. Sloan Foundation.

Media Contacts

Josie Garthwaite, School of Earth, Energy & Environmental Sciences: (650) 497-0947,

Adam Brandt, School of Earth, Energy & Environmental Sciences: (650) 724-8251,