British Gas has apologised after mistakenly charging a Bristol customer £17,000 for a £170 electricity bill.
The money was charged to Tony Leventhal's credit card and was only picked up when his bank contacted him.
A data input error put two extra zeros on Mr Leventhal's bill, British Gas said, which has now been corrected.
A company spokesman said: "The vast majority of transactions go without a hitch, but obviously this one didn't and we would like to apologise for it."
"British Gas apologises to Mr Leventhal for this billing error," he added.