Bankruptcies among oil and gas companies have reached quarterly levels last seen in the Great Recession, according to the Federal Reserve Bank of Dallas.

At least nine U.S. oil and gas companies that accounted for more than $2 billion in debt have filed for bankruptcy in the fourth quarter, the bank said Wednesday in its energy economic update for the final three months of the year.

"Lower oil prices have taken a significant financial toll on U.S. oil and gas producers, in part because many face higher costs of production than their international counterparts do," according to the note written by Navi Dhaliwal, a research assistant, and Martin Stuermer, a research economist. "If bankruptcies continue at this rate, more may follow in 2016."

Since peaking in October 2014, U.S. oil and gas employment has fallen by 70,000 jobs, the analysts wrote in the report.