The new bio-gas double deck buses will operate on Brown 15, 16, 17 routes between Nottingham and Bulwell, Top Valley and Rise Park, Orange 35, 36 between Bulwell and Nottingham and Lime 56, 57, 58, 59 between Arnold and Nottingham.
The new buses are the first of 23 ordered as part of £7m, investment by NCT and all are expected to be in service by the end of August.
NCT already operates the world’s largest fleet of bio-gas double decks in the world at 120 buses.
Bio-gas is produced naturally through anaerobic digestion, using food waste, farm waste and sewage.
The methane emitted from the digestion process is captured, treated and turned into fuel and the use of bio-gas has enabled NCT to halve its diesel consumption from eight million litres to four million per year.
The bio-gas buses already run on three quarters of NCT’s double-deck services and the current fleet has clocked up more than 15 million miles in service since first appearing on Nottingham’s streets five years ago, in July 2017.
In the process, they have prevented 26,000 tonnes of carbon dioxide being emitted, as well as reducing nitrous oxide emissions by 180,000kgs.
Liam O’Brien, NCT’s head of engineering, said, “NCT is committed to minimising its impact on the environment and we already operate one of the greenest bus fleets in the country.
"Our bio-gas fleet has contributed to much improved air quality in and around Nottingham and this investment will improve it further”.
The engines and chassis of the new buses have been developed by Swedish giant Scania and are bodied in Britain by Alexander Dennis Limited (ADL).
Mark Oliver, sales director for bus, coach and power solutions at Scania UK, said: "This project is a culmination of seven years hard work between NCT, ADL and Scania.
"At Scania, we are committed to help businesses decarbonise their operations, which is why we are proud to see this project come to fruition.”
Lee Salt, sales account manager covering the Midlands and Wales at ADL added: “We are delighted to support Liam and the team at NCT on their journey to delivering more sustainable transport.”