A small energy supplier based in Birmingham with more than 100,000 customers has ceased trading.
Extra Energy, which is headquartered in Edgbaston, was one of a clutch of new suppliers to enter the market in recent years.
But the company, backed by Israeli businessman Moti Ben-Moshe, has ceased trading and financial services PwC is expected to be appointed administrator to the firm.
Extra Energy has around 108,000 domestic and 21,000 business customers and launched here in 2014.
We reported in September 2016 that Extra Energy had attracted the highest number of customer complaints among energy companies for a second consecutive quarter, according to research from Citizens Advice.
But just weeks later, Extra Energy announced it was planning create 50 new jobs at its base in Hagley Road, on the back of 550 new hires it had made over the previous 18 months.
Under regulator Ofgem's so-called "safety net" procedure, the energy supply of Extra Energy's customers will continue as normal and outstanding credit balances will be protected.
Ofgem will choose a new supplier to take on its customers as quickly as possible which will then contact customers shortly after being appointed.
Future Energy, Iresa Energy, Gen4U and Usio Energy have also all gone bust in 2018.
Extra Energy's website is now just a holding page with information for customers.
It says: "Extra Energy Supply Ltd will be ceasing to trade.
"Ofgem, the energy regulator, is appointing a new supplier for its customers. The credit balances of domestic customers are protected.
"Ofgem's advice is not to switch, but to sit tight and wait until the new supplier has been appointed.
"This will help make sure that the process of handing customers over to a new supplier, and honouring credit balances, is as hassle free for customers as possible."
The market has been hit by stinging regulation, including a government-enforced price cap on standard variable tariffs amid anger over rising bills.
The failure comes as Ofgem announces that new energy suppliers entering the market will have to show they have adequate financial resources and can meet customer service obligations.
Ofgem said the tests should ensure new entrants were robust while encouraging competition and innovation in the market.
Applicants for new supply licences will have to demonstrate to Ofgem they have the funds and resources to manage their business for at least 12 months after entering the market.
Philippa Pickford, Ofgem's interim director for future retail markets, said: "If you are an Extra Energy customer, under our safety net, we will make sure your energy supplies are secure.
"We will also ensure that domestic customers' credit balances are protected. Ofgem will now choose a new supplier and ensure you get the best deal possible.
"You can continue to rely on your energy supply as normal.
"We will update you when we have chosen a new supplier who will then get in touch about your new tariff."