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The central bank said it sold $37.4 million at a cut-off price of 7.1401 pounds per dollar, unchanged from its last sale on Wednesday.
The rate for the dollar sales has stayed in a very tight range since the beginning of June, after the bank allowed the pound to weaken in May. It had offered $40 million on Thursday.
On the black market, the dollar changed hands for 7.42 pounds, one market participant said, weaker than Wednesday's rate of 7.38/40.
The rates at which banks are allowed to trade dollars are determined by the results of the central bank sales, giving the bank effective control over official exchange rates.