British Gas is to extend a price freeze for customers on its standard energy tariff until August, while ScottishPower has announced a 7.8% rise in standard gas and electricity bills.
A statement from British Gas owner Centrica said the freeze has been made possible "despite increases in external costs".
Boss Mark Hodges said: "We're pleased to give our customers on standard tariffs the peace of mind that the price they're paying will remain unchanged until August.
"We are determined to give our customers great offers and services. In December we promised to take tangible action to improve how the energy market works for all our customers. That effort continues.
"We aim to do even more in the coming months to meet our customers' needs, earn their business, and reward their loyalty."
But while British Gas customers were breathing a sigh of relief, ScottishPower's were not so fortunate.
The Big Six firm is to hike its standard gas and electricity prices by 7.8% following "rises in energy wholesale markets and compulsory non-energy costs".
These include costs for decarbonising electricity generation and an upgrade to smart meters, ScottishPower said.
The move will hammer 1.1 million of its customers and see electricity prices rocket by an average of 10.8% and gas prices by 4.7%.
Colin McNeill, the firm's UK retail director, said: "We continue to work hard to move even more customers to our fixed-price deals. We will be writing to all those affected, outlining the changes and encouraging more loyal customers to move to a deal that best suits them.
"This price change follows months of cost increases that have already led to significant rises in fixed-price products that now unfortunately have to be reflected in standard prices."
Last week Npower came under fire from the Government and the energy regulator after announcing plans to hike gas and electricity prices by 9.8% - a move that will add £109 to annual dual fuel bills.
It comes after rival EDF increased prices in December, and experts believe more energy providers will now follow suit.
Consumers are already expecting to be battered by soaring prices this year after the country voted for Brexit, resulting in the collapse in the value of the pound.
The result has been rising price inflation, which hit a two-and-a-half-year high of 1.6% in December. It is expected to rise further over 2017 as the cost of imports soar on the back of the British currency's fall.