Customers of Green Star Energy are set to move to Shell Energy, bringing the challenger brand to nearly one million customers.
The deal, announced yesterday, is for Shell Energy Retail to buy Green Star Energy's parent company, Hudson Energy Supply. It is expected to be completed by the end of the year, as long as the merger is approved.
Shell Energy is already one of the biggest brands outside of the Big Six, with around 780,000 customers.
This is far from the first merger between challenger brands: Octopus begun supplying Co-operative Energy customers in July, while SSE is selling its household energy business to Ovo.
If you're a Green Star Energy customer, you will continue to be supplied by Green Star until the deal completes. This is expected to be by the end of the year.
The terms and conditions of your tariff won't change even when the deal is complete, both Green Star Energy and Shell Energy have said.
You will also still get Perks Rewards - points awarded every three months for customers on eligible tariffs which can be exchanged for gift cards and smart energy efficiency products.
Shell Energy's overall customer score was just one percentage point higher (66%) than Green Star Energy's (65%). They finished joint-16th and 19th respectively out of 30 energy firms.
The top-scoring firm in our survey scored 80%, while the lowest achieved just 44%
However, Shell Energy customers rated the accuracy of its bills, online customer service and phone customer service slightly better than Green Star Energy's customers did.
*The survey was conducted before First Utility had re-branded to Shell Energy.
At the moment, Shell Energy is selling the cheaper energy deal of the two companies. It costs £1,059 per year for a household using a medium amount of energy. Green Star's cheapest deal costs around £91 more per year.
If you didn't pick a new tariff when your last fixed deal ended, you'll be on your supplier's standard or default tariff. The firms are charging the same for these: £1,178 per year. There is currently a price cap on these types of tariffs and both are charging within £1 of the maximum permitted.
How much you're paying depends on the tariff you are on, and how much gas and electricity you use. Check your online account or annual statement to see this information, then use a comparison site, such as , to compare prices. Make sure you use your actual energy use in kWh to get an accurate quote.
Prices are based on a dual-fuel tariff, paying by monthly direct debit, with paperless bills.
Energy use is based on Ofgem's annual average figures for a medium user (12,000kWh gas and 3,100kWh electricity per year).
Data is from Energylinx. Price given are averages across regions in which they are available, rounded to the nearest whole pound and correct on 9 October 2019.