The study, by LobbyFacts, a lobby data website, suggests that out of the 51 organisations declaring the highest lobby spend "only 12 are likely to, in fact, be among the biggest lobbyists."
"There is only one reliable-looking entry among the 30 entries declaring the highest lobby spend," says LobbyFacts.
The group produced the list by cross-referencing declared expenditure with the number of meetings held with senior staff at the Commission and the numbers of European Parliament passes held.
It says these are good indicators of an organisation's actual lobby activity.
Erik Wesselius, a spokesperson for LobbyFacts, said the survey highlights the excessive influence that corporate lobbyists can have on political decisions that affect people's lives - including TTIP, tax fraud, data privacy and climate change.
"The pollution of the register by inaccurate entries, whether over-reporting or under-reporting lobby spend, is endemic," he says.
"The only solution to this is to get tough: implement a legally-binding lobby register with the ability to apply sanctions so that there is a real disincentive to post inaccurate data. The Commission has tried the carrot approach since 2008; now it is time for the stick."
According to LobbyFacts some of the "world's biggest corporate interests" such as Exxon, Shell and Microsoft, appear as "top-spending EU lobbyists" as well as trade associations representing the chemicals, finance, insurance and pharma industries.
Three lobby firms also appear on the LobbyFacts list: Fleishman-Hillard, Burson-Marsteller and Interel.
Of the top 12 highest spending lobby organisations, 11 of them (92 per cent), are said by LobbyFacts to represent corporate interests and between them they reportedly spent €72,012,760 in the most recently declared year.
Between them, LobbyFacts say they held 228 meetings with senior Commission officials since December 2014 and hold 192 European parliamentary access passes.
Wesselius said, "More lobby transparency is needed but the EU institutions also need to end the privileged access that corporations and corporate interests currently enjoy."
The Commission has proposed to introduce a mandatory lobby register and is inviting all Europeans to take part in a survey and submit their ideas on how to improve lobby transparency in the EU.
The deadline for contributions is 31 May.
A spokesperson for the Europe-wide Alliance for Lobbying Transparency and Ethics Regulation (ALTER-EU) and Democracy International said, "We need to use this opportunity to demand clear and strict rules that will prevent secret lobbying in the future.
"Over 25,000 lobbyists go in and out of the European institutions in Brussels every day to influence EU politics. We citizens have no access to information about which politicians they meet, what issues they try to influence and how many billions they spend on it. This is a threat to our democracy."
Meanwhile, the Council has indicated it is open to adopting new lobbying disclosure rules, but a top diplomat warned that striking a deal with other EU institutions will be difficult because of fears of "transparency mission-creep."
The LobbyFacts analysis comes in the wake of a recent Commission and Parliament event to debate the future of the lobby register, as part of the consultation on transparency.
Speaking in Parliament at the forum on transparency reform, Dutch EU ambassador Pieter de Gooijer said member states had to be involved in the development of a revamped transparency regime.
It is the first indication the Council would consider signing up to lobbying disclosure rules by reaching an agreement with Parliament and the Commission, which already have transparency requirements in place.
But de Gooijer said some countries remain opposed to extending lobbying rules to cover their permanent representations.
A recent study by a coalition of transparency NGOs found that the permanent representations, which are not subjected to any transparency requirements, are heavily lobbied.
Commission First Vice President Frans Timmermans told the meeting that any future deal was likely to involve the three big EU institutions - a single code of conduct for EU officials.
"Our best option of getting the three institutions in a position to enhance transparency is to go for an inter-institutional agreement," Timmermans said.
The Commission and Parliament have operated a voluntary joint transparency register since 2011, which was designed to identify the names of lobby firms, trade associations, NGOs and individuals who are lobbying the EU institutions.
In 2014,new rules were brought in which prevented commissioners, their political staff and top-level public servants from meeting lobbyists who were not signed up to the register.
The 2014 changes also required that meetings with lobbyists be disclosed on the Commission's websites but, to date, the register remains voluntary.