The leader of the Welsh national party, Plaid Cymru, has signed up in support of PetrolPromise.com.
Elfyn Llwyd is the 69th MP to back the campaign website’s push for an Office of Fair Trading (OFT) investigation into the price of fuel.
PetrolPromise, which was founded by Robert Halfon MP, wants the non-tax element of the price of fuel reduced.
As well as an OFT investigation, it is calling for a Royal Commission to be set up to investigate how fuel prices can be reduced.
Earlier this month the website passed 1,300 signatures of support from members of the general public via an e-petition.
Halfon also recently made the case in Parliament for pump prices to be made more transparent.