Last year, the number of vehicles in the UPS fleet that run on alternative fuels topped 5,000.

This is according to the latest data published as part of the package carrier's 13th Annual Sustainability Report. 

It was specified that this constitutes the addition of 1,100 natural gas vehicles and represents a 61 per cent increase in the number of environmentally friendly vehicles in the firm's fleet. 

A total of 5.4 per cent – or 25 million gallons – of UPS's total gas and diesel purchased in 2014 was displaced with alternative fuels. 

The company hopes to use these to cut its annual gasoline use by 12 per cent before 2017 - and some of the fuels it is using instead include natural gas, propane, ethanol, biomethane, renewable diesel, and electricity.

UPS chief sustainability officer and vice-president of environmental affairs Rhonda Clark said: "With continued investments in this fleet, we are doing our part to help transform the transportation industry."