Free swimming in Oxford pools could be limited to young swimmers who live within the city boundaries.
The city council believes it is now subsidising children from outside the city to the tune of £38,000 a year.
Legal officers have been asked to investigate whether swimming and possibly other free services may be offered exclusively to Oxford residents.
Previously, it was thought that a European Court ruling might result in any 'for Oxford residents only' policy being legally challenged, on the grounds of unfair discrimin- ation.
But with the council anxious to make savings in leisure spending to help recoup more than £5m in next year's budget, councillors want to re-examine the issue.
One option being considered is the idea of introducing an 'Oxford Card', that residents would have to show to use free or subsidised services.
Exeter City Council, in Devon, has introduced a leisure card "to give savings and benefits to local people" covering its leisure and museum services.
Offering all under-17s free swimming in Oxford's indoor and outdoor pools will cost the council £375,000 over the three years the scheme is to run.
Charges of £1.70 per child were dropped last year at pools in Blackbird Leys, Summer- town, Temple Cowley, Barton, Littlemore and Hinksey.
The council said the policy would encourage more children to exercise and learn to swim, seen as important in the aftermath of several local drow- nings.
Deputy council leader David Rundle said: "It's really about the issue of making sure we're giving value for money to local council tax payers.
"A free service for everyone means that Oxford council tax payers are subsidising the others.
"So we're looking at this situation. We need to know exactly what the legal situation is.
"Personally, I would be very interested in the idea of an Oxford Card being introduced for Oxford residents, which could involve a whole range of different things."
Earlier this week, the council said it was considering reducing the water temperature in pools in order to save money.
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