Redman Jones & Partners and MediaVest Manchester have also worked on below-the-line Transco projects.
A Transco spokesperson said that its decision to review the business came as part of a statutory process that occurs every three years.
Transco traditionally concentrates its advertising around a safety awareness campaign at Christmas to remind the public that its gas emergency service operates 24 hours a day, seven days a week.
Last year saw the return of the sniffing snowman and Rudolph slippers television commercials.
These were supported by press ads in television listings magazines and regional newspapers. Last year also saw the first television campaign targeted at Asians, which made no references to Christmas, and ran on the specialist Asian channels.
The spokesperson added that Transco would be extending its advertising to run throughout the year.
Transco is responsible for the delivery and maintenance of gas supplies and for providing emergency cover. It demerged from British Gas in October 2000 and delivers gas which has been bought from retailers such as Centrica and London Electricity.
Transco is now the major component part of the Lattice telecommunications group, which supplies fibre optics and mobile telecoms tower networks.
Lattice recently merged with National Grid.