The Office of Fair Trading has taken action against two heating oil companies and price comparison websites it says were "misleading" customers.

An OFT investigation has found that some websites offering to find consumers the best price for heating oil were not clear about whether they were price comparison sites, or sites for ordering heating oil directly from a single supplier.

The OFT has secured undertakings under the Consumer Protection from Unfair Trading Regulations (CPRs) from WCF Fuels Limited and Boiler Juice Limited, preventing them from engaging in business practices that could be misleading.

•, operated by Boiler Juice Limited, is a price comparison website providing price quotations from GB Oils Limited as well as price quotations from other non-related heating oil distributors. The OFT found that was not transparent about its links to parent company DCC plc, which owns GB Oils Limited, the largest heating oil distributor in the UK.

The businesses investigated have co-operated with the OFT's investigations and voluntarily made changes to their websites.

The investigation was carried out in connection with an OFT market study into the supply of energy to the four million households who are not connected to the mains gas grid. The outcome of this study will be published in October 2011.

Clive Maxwell, executive director at the OFT, said: "Our investigation has aimed to ensure that any relationships between businesses supplying heating oil and websites are transparent and that the number of prices that have been compared by the website is stated prominently.

"It is important that people can genuinely shop around and make informed decisions about which suppliers to use. The changes that we have secured mean that people buying domestic heating oil will be better able to compare deals on offer."