This came after all global ratings agencies expressed concern over how it would raise money to pay for its new projects.
Africa's biggest electricity generator applied for an 18,7% price increase to the National Energy Regulator of South Africa.
Eskom was hurrying to bring new capacity on stream, with reserve margins sitting at levels near zero. It already planned to spend around R300-billion over the next few years.
"Eskom will need to borrow more than if it had been granted the 18,7%," FD Bongani Nqwababa said in an emailed statement. "In addition, the current electricity prices are unsustainable, and will result in steeper increases being required in the near future."
On Monday, CEO Jacob Maroga told reporters that the utility would need to hike prices by double digits for some time to come.
Eskom said that in addition to its capital expansion programme, fuel costs had risen over 30% in 2007.
"Further, the cost of plant and equipment has risen from by 20% to 50% in the past year, and has doubled in five years," the company said. "The increase applied for is therefore necessary given the circumstances."
"The lower price increase will make it even harder for Eskom to satisfy conditions in the current financial markets to assure the funding needed for the capital expansion programme to ensure security of supply," Nqwababa said.
He told Engineering News Online the previous day that the utility had met with the National Treasury last week to discuss possible funding options.