The company is owned by Hugh Morgan, the convicted fuel smuggler who revealed that Mr Gallagher invited him to a €5,000-a-head Fianna Fail fundraiser.
Mr McGuinness's disclosure of the revelation during a live presidential debate on RTE's 'The Frontline' helped to scupper Mr Gallagher's campaign for the presidency.
Figures for spending by Sinn Fein's candidate, released yesterday, show three separate payments to Morgan Fuels -- €948, €765 and €1,156 -- adding up to a total of €2,869.
He also ran the most cost effective campaign, which only cost him a net €40,000, once the takings from donations and the reimbursement from the taxpayer were taken into account.
After Mr Mitchell, Mary Davis spent the second largest amount at €414,000 -- this was the largest by an independent candidate.
The spending limit per candidate was €750,000. Only three of the seven candidates qualified for the reimbursement of election expenses of €200,000 -- Mr Higgins, Mr Gallagher and Mr McGuinness -- by getting over 12.5pc of the vote.
Candidates had to declare any donations over €638 and were only allowed to accept donations of up to €2,540.
Tanaiste Eamon Gilmore was among Mr Higgins' donors, giving his campaign €2,000.
Labour appeared to have a sliding scale for donations from politicians, with cabinet ministers giving €2,000, junior ministers €1,500, TDs €1,000 and senators €750.
Mr Higgins also got €1,250 from former Attorney General John Rogers, €2,000 from consultancy firm, Farrell Grant Sparks, as well as €2,000 from Greg Sparks and €1,500 from Maurice Cassidy, both of whom work for the company.
Ms Davis received the second-largest amount of donations. She received contributions from businessmen Denis O'Brien of Digicel Group (€2,500), who worked with her on the Special Olympics; Dermot Desmond of IIU (€2,500); and Richard Barrett of Treasury Holdings (€2,000).
Mr Desmond also gave a donation of €2,000 to David Norris. Mr Norris received a €2,500 donation from the Riverdance creator John McColgan.
Mr Gallagher received donations of €2,500 from Senator Feargal Quinn, businessman Gerry McCaughey and Harmonia, the company owned by 'Dragons Den' panellist Norah Casey.
Mr Mitchell spent just under €160,000 on election posters, more than any other candidate.
Mr Norris spent almost €1,300 on "pottery" and another €2,100 on printed t-shirts and balloons. He also spent €3,800 on "preparation of campaign bus including painting and graphics".
Mr Gallagher spent €4,533 on "publicity" with Screentime Shinawil -- the company that make the 'Dragons' Den' show on which he was a panellist.
Mr Higgins spent €1,089 on his own private "research poll" carried out by Millward Brown Lansdowne.
Ms Davis spent a combined €9,200 on professional photography and Ms Scallon spent €2,043 with Hertz Rent a Car.