Petrol and diesel prices at Asda Merthyr Tydfil Superstore

Asda Merthyr Tydfil Superstore, CF48 2YF.

What it is charging

Unleaded: 171.9p a litre, 0.2p over the national average, filed Thursday 29 October
Diesel: 197.9p a litre, 0.8p under the national average, filed Thursday 29 October

Tredegar Service Station: 168.9p a litre, 4.1 miles away. 3.0p a litre cheaper: saves £1.65 a tank, and costs about £1.57 of fuel to get there and back. Worth the trip.
Rhymney Service Station: 170.9p a litre, 2.4 miles away. 1.0p a litre cheaper: saves 55p a tank, and costs about 93p of fuel to get there and back. Not worth the trip.
EG Merthyr Tydfil Pfs: 172.9p a litre, 2.4 miles away
Rontec Dowlais: 174.9p a litre, 1.2 miles away
Ambay Service Station: 176.9p a litre, 3.6 miles away

On a 55-litre tank at 40mpg. The distance is straight-line rather than by road, so a real trip is longer than the one costed here.