The research company says that while internet adspend is going to rise to €4.7bn (£3.3bn) in Europe over the next five years, marketers are likely to find that the cost of participation is also rising.
JupiterResearch says that the growth will be driven by increasing numbers of European consumers with internet access and growing broadband penetration.
As well as rising costs, Jupiter says that marketers will find that the growing scope of online marketing will call for greater time and effort to be spent managing campaigns.
Julian Smith, author of the report and analyst at JupiterResearch, said: "Not only will the price of online real estate grow, but as marketers develop in sophistication and the scope and scale of their online campaigns augments, so the resource requirements to optimise the online mix will burgeon.
"As a result, marketers will need to look to new tactics and technologies to improve the targeting and impact of their campaigns in order to improve return on investment."
The report forecasts a 29% rise in internet adspend across Europe in 2005 to €2.7bn.
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