Highways England will trial fuel price displays on a southbound section of the M5 motorway from next year.
The move is part of a push to give drivers more information when on the road, and to boost fuel price competition, as high prices at motorway service areas have come in for criticism from several motoring groups.
Five service areas between Bristol and Exeter are involved in the test, which will run until the end of 2017.
Signs will show the price of fuel at Gordano, Sedgemoor, Bridgwater, Taunton Deane and Exeter service areas.
"The Government is on the side of the honest motorist who have raised concerns for too long about petrol prices at motorway service stations. This trial will allow drivers to be much better informed about the cost of fuel and make it easier to plan their breaks around the cheapest deals," said roads minister, Andrew Jones.