The Reserve Bank will shortly release the results of a study into the gap between the central bank's main interest rate and prime-rate borrowing costs but is not formally investigating collusion between commercial banks, Finance Minister Pravin Gordhan said yesterday.

The sector is dominated by four banks - Standard, Absa, Nedbank and FirstRand - and has been criticised for being uncompetitive.

On Tuesday, Dominique Strauss-Kahn, managing director of the International Monetary Fund, said more competition should be introduced into the banking sector to help tackle inflation.

"The Reserve Bank has indicated to the Treasury that there is no investigation on interest rates charged by commercial banks," Gordhan said in response to a written question in parliament.

"Instead, there is a joint committee to discuss the spread between the repurchase rate and the prime lending rates ... and their report will be made public very shortly, within one or two months," he added.

The joint committee of members of the central bank and of the Banking Association of SA was formed in May after former central bank governor Tito Mboweni questioned the steady 3.5 percentage point gap between the Reserve Bank's base rate and bank's prime rates.

The repo rate is at 7% and prime is at 10.5%.