Oxfordshire CC has suggested 85% of the county's 30mph roads could be reduced to 20mph, as part of a programme kicking off in the village of Cuxham this month.
A potential county-wide programme could reach the 85% figure, subject to public support and funding, the council said.
It is also consulting on four more 20mph trial sites in Long Wittenham, Wallingford Central, Wallingford North and Kirtlington.
The introduction of the 20mph limit pilot in Cuxham was approved following a consultation in which 82% of respondents were in favour of the speed reduction, the council said.
Cllr Tim Bearder, Oxfordshire County Council’s cabinet member for highways management, said: 'Oxfordshire people want to revolutionise our residential areas and turn them back into safe and attractive places for people to walk and cycle.
'Residents of five determined and forward-thinking villages have volunteered to be a test bed for a suite of measures based around the introduction of 20mph speed limits. This important and detailed work will help us develop a plan to really deliver the results people are increasingly telling us they want to see.'
The Cuxham trial will initially consist of 'signs only to see if drivers’ behaviour alone will reduce speeds in the areas'.
If not, then low-cost traffic calming measures will be experimented with, the council said.
'This 20mph approach is required in Oxfordshire if we are to deliver our vision to make active travel, public and shared transport the natural first choice,' added Cllr Bearder.
As part of the process, Oxfordshire CC said it would work with the campaign group 20’s Plenty, local communities, Thames Valley Police, bus companies and other stakeholders.