Leasing company Arval said the average CO2 emissions of cars delivered to its customers was 114g/km in 2014, a fall of 7% compared to figures from 2011.
The firm said its results are favourable compared to the market in general. The BVRLA's Quarterly Leasing Survey suggested the national average emissions for new vehicles registered were 123.8g/km CO2.
Most fleets should have a cut-off of 130g/km CO2, due to capital gains allowances.
Arval said the number of hybrid and electric vehicles leased to customers increased from 888 in 2013 to 1081 in 2014.
"With vehicle costs and CO2 emissions going hand-in-hand, the environmental performance of the fleet is often a high priority for our customers. We spend a lot of time working with them to deliver the most sustainable and cost effective fleet policy for their business," said Robert Pieczka, director of corporate social responsibly at Arval.
It recently reached 100,000 funded vehicles in the UK for the first time.
The firm said the growth was down to new products and initiatives including the Smart Service range and the Total Care option.
"Since I joined Arval just over a year ago we have had a clear growth strategy, underpinned by a focus on customer service and the development of our employees," said Benoit Dilly, managing director of Arval UK.