According to the release, OU and Texas sent SEC commissioner Greg Sankey their request Tuesday morning.
"The two universities look forward to the prospect of discussion regarding the matter," the statement read.
According to the letter, which was dated July 27 and made public, Texas president Jay Hartzell and Oklahoma president Joseph Harroz Jr. wrote, "We believe that there would be mutual benefit to the Universities on the one hand, and the SEC on the other hand, for the Universities to become members of the SEC."
Sources said the SEC presidents and chancellors are meeting Thursday to consider OU and Texas for official membership in what would become the first 16-team superconference. In spite of the formal notification from the Big 12 schools, a source familiar with the process cautioned that it still doesn't guarantee the SEC will vote at that time. A three-fourths majority vote of SEC presidents and chancellors (11 of 14) would be required for invitations to be extended.
Sources previously told ESPN that it's believed enough SEC schools will vote to add the two new members.
"While the SEC has not proactively sought new members, we will pursue significant change when there is a clear consensus among our members that such actions will further enrich the experiences of our student-athletes and lead to greater academic and athletic achievement across our campuses," Sankey said in a statement. "The Presidents and Chancellors of the SEC, in their capacity as the conference's Chief Executive Officers, will consider these requests in the near future."
The boards of regents for both Texas and Oklahoma have scheduled separate special meetings Friday morning, during which athletic conference membership will be discussed. Oklahoma's regents will meet in Oklahoma City, while Texas' regents will meet via conference call.
Texas and OU stated in the letter that they intend to remain in the Big 12 through June 30, 2025, because that's when the current Big 12 media rights deal expires -- but that doesn't guarantee they won't find a way to leave before then. If it happens earlier, each university would have to pay a penalty of at least $75 million to $80 million to break that agreement, or hope that the Big 12 dissolves before the grant of rights contract expires.
Big 12 commissioner Bob Bowlsby issued a statement Tuesday saying that the conference would "face the challenges head-on."
"The events of recent days have verified that [Texas and Oklahoma] have been contemplating and planning for the transition for months and this formal application is the culmination of those processes," Bowlsby's statement said. "We are unwavering in the belief that the Big 12 provides an outstanding platform for its members' athletic and academic success. We will face the challenges head-on, and have confidence that the Big 12 will continue to be a vibrant and successful entity in the near term and into the foreseeable future."
One Big 12 source suggested the possibility that OU and Texas are banking on a relationship that turns so sour over the next few years, the Big 12 agrees to cut them loose for less.
A source within the SEC said the Longhorns and Sooners "have a lot of legal work to do before they can just walk over to us."
ESPN's Adam Rittenberg and Mark Schlabach contributed to this report.