A spokesman in the office of Pruitt's successor, Mike Hunter, told Oklahoma City's Fox 25 that Pruitt had used his personal email account when he worked there.
Pruitt was Oklahoma's top attorney from 2011 until the Senate confirmed him last week to be President Trump's EPA head.
Fox 25 discovered the email address in a public records request. The documents it received contained a redacted address, which Lincoln Ferguson, a spokesman for the office, said was a personal account that had been searched for the station's request.
The redacted address also appears in the thousands of pages of emails that Oklahoma released this week detailing Pruitt's and his aides' communications with energy companies and conservative groups, among others.
Pruitt had told the Senate Environment and Public Works Committee last month, as part of his confirmation process, that he had a personal email account, but he never used it for official business.
Using a personal email address for official business does not violate Oklahoma's laws regarding government records.
Hillary Clinton, the unsuccessful Democratic candidate for president in last year's election, famously used a private email address on a privately run server for official business when she was secretary of State, a setup that played a key role in the 2016 presidential election.
Federal employees are not legally prohibited from using personal email accounts for business, but they must quickly copy the emails to a government system for record-keeping and transparency purposes.
Lisa Jackson, EPA administrator from 2009 to 2013, used an email address within the government system with a pseudonym, "Richard Windsor."
Senate Environment and Public Works Committee Chairman John Barrasso (R-Wyo.), brought up Jackson's email address at Pruitt's confirmation hearing, and asked Pruitt if he would "refrain from taking any such action that makes it difficult or impossible for the public to access your official written communications under the Freedom of Information Act."
Pruitt said "yes," and added that he believes transparency is important.
