Alan Horowitz discusses the Tax Court's February 3 decision in Exxon Mobil Corp. v United States, which rejected the Internal Revenue Service's longstanding interpretation of the special rule governing retroactive application of Code section 6621(d), legislation passed in 1998 that eliminated the interest rate differential on overlapping periods of interest on overpayments and underpayments. "Certain taxpayers who were in an interest netting situation prior to July 22,1998 can cite this decision in support of a claim to recover interest that they paid for periods when they had no net tax due," said Horowitz, who represented Exxon Mobil. According to Horowitz, the Tax Court also correctly ruled that interest netting claims can come within that court's limited authority to determine interest issues. "Although an interest netting claim clearly involves an interest rate determination, the IRS had argued that such claims seek a special form of relief that is outside the court's jurisdiction," Horowitz said.