With a carbon intensity of 0.85 tons of carbon dioxide equivalent per $1 million of revenue, Aviva tops the ET Europe 300 Carbon Ranking compiled by the non-profit group the Environmental Investment Organization.
Telecoms company Swisscom, Deutsche Bank and Finnish cellphone maker Nokia also managed to get high in the rankings due to low total emissions and their transparent reporting.
The most climate-intense company is International Power, a multinational energy provider that produces 11.182 tons of CO2 equivalent per $1 million of revenue.
Eon from Germany, one of the world's largest utilities, amassed the most total emissions, with a yearly output of 164.8 million tons of CO2 -- roughly the same as Venezuela's in 2007.
Eon, which relies heavily on coal-fired power plants, trumped steel maker ArcelorMittal and RWE, another coal-intense utility from Germany, which came in second and third with 164 million and 152 million tons, respectively. (Both Eon and RWE have said they want to drive down their emissions.)
In the overall rankings, Eon stands at position 120, ArcelorMittal at 121 and RWE at 127, because of the high turnover they generate and their commendable reporting behavior.
That's certainly not the case for all companies. The study found that 38 out of the 300 firms didn't disclose their total CO2 emissions or that the data published were unclear.
They include a number of potential carbon heavyweights such as Parmalat, Italy's biggest listed food group, as electrical equipment company Schneider Electric and Veolia, the world's largest water and sewer service provider, both from France, and oil giant BP.
"Despite most companies producing corporate social responsibility reports there remains a remarkable lack of transparency and clarity in greenhouse gas emissions reporting," Sam Gill, the director of the EIO, said in a statement.
The purpose of the rankings was two-fold, he added.
"To highlight the carbon emissions and levels of disclosure of the world's largest companies with the aim of fostering greater transparency and to form the basis of a series of stock market indexes, designed specifically to provide the investment community with a viable tool for tackling climate change," he said.
The EIO said it plans to publish regional rankings for North America, Asia-Pacific and BRIC nations, as well as a global score sheet.