The report, which was conducted by New Media Agencies Financial Intelligence, found that UK digital agencies have benefited from rationalising their existing operations into a single company.
However, the study noted a "diversity of performance" among the top 40 agencies. The reasons given for underperformance included the reluctance of agencies to charge clients the correct fees, and over dependence on expensive freelancers.
G2 Interactive was listed as the most profitable agency for the second year running, generating an operating profit per head of £33,322; followed by ILG Digital in second place on £27,997; Start came in third with £25,001; and Outrider fourth on £24,508.
Completing the top 10 were Win in fifth; AvenueA in sixth; Poke London seventh; Agency Republic eighth; iTouch ninth; and Netstore 10th.
New Media Agencies Financial Intelligence said five agencies involved in differing segments of the digital market achieved "excellent" operating profit margins of 20% or more, but 25 companies had margins below 10%.
In addition, Deal Group Media, Green Cathedral and Twentysix London returned operating losses, and were placed 40th, 39th and 38th respectively in the report.
The report commended productivity levels at iTouch, LBi, Poke London, G2 Interactive and Conchango -- where in each case revenues per head exceeded £95,000 and staff costs were kept below 53% of those revenues.
Other agencies were noted for correcting the causes of past inefficiencies, but the report warned that "far too many" agencies were not reaching their full potential.
Bob Willott, editor of the report, said: "Profit margins and staff utilisation levels varied enormously from the impressive to the depressive."
The report added that staff costs ate into a disproportionately large portion of revenues, averaging 57.1% among marketing agencies and 53.4% overall.
The full report is available from the New Media Agencies Financial Intelligence .