CNG Energy has become the 20th energy provider to stop trading this year, affecting more than 40,000 customers.
CNG supplies energy to around 41,000 businesses and is the latest victim of the energy crisis.
A statement on the CNG website said: "After 27 years we are saddened to say CNG Energy Limited is ceasing to trade.
"Ofgem the energy regulator is appointing a new supplier for CNG customers.
"Customers need not worry, their supplies are secure and funds that domestic customers have paid into their accounts will be protected if they are in credit."
Ofgem director of retail Neil Lawrence said: "Ofgem’s number one priority is to protect customers. We know this is a worrying time for many people and news of a supplier going out of business can be unsettling.
“I want to reassure affected customers that they do not need to worry under our safety net we’ll make sure your energy supplies continue. "
Yesterday gas and electricity suppliers Omni Energy, MA Energy, Zebra Power and Ampoweruk Ltd all stopped trading.
Regulator Ofgem announced the four suppliers had entered administration on Tuesday.
Omni Energy supplies around 6,000 domestic pre-payment customers, Zebra Power supplies around 14,800 domestic customers and Ampoweruk Ltd supplies around 600 domestic customers.
The failed company also supplies around 2,000 non-domestic customers.
MA Energy – the smallest of the four - supplies around 300 non-domestic customers.
The total number of affected households across the four firms is 23,700.
Ministers and industry regulator Ofgem are understood to be in talks over the future of Bulb - which has around 1.7 million household customers.
Sources told the broadcaster the firm could collapse as early as next week if it fails to secure a buyer.
Industry sources said on Friday that talks with a small number of potential buyers were ongoing, but that others had pulled out in recent days.
What to do if you are a CNG customer
If your energy firm collapses, the advice from Ofgem is to sit tight and wait until your new supplier contacts you.
You should wait until you know which firm you've been moved to before you decide to look into switching elsewhere.
In the meantime, take a meter reading for when your new supplier contacts you so it can correctly bill you.
It is important to check prices as soon as you know which deal you've been moved to, as you may not necessarily be transferred over to the cheapest supplier.
You won't be charged exit fees for switching away from your new energy provider.
However, just because you're moved to a new energy supplier doesn't mean it is as good a price as you had with your old firm.
You do not have to accept the new provider just because they contact you. If the deal looks pricey you are still free to shop around for a new one.
But remember that energy prices are going up generally, and deals are not as cheap as they once were.
