* Opinions of court advises tend to reflect final decision
* Carbon market not expected to react
* Case closely watched by industry
By Barbara Lewis
BRUSSELS, Nov 9 (Reuters) - A top EU court adviser will on Thursday deliver an opinion on whether the European Commission's calculations to decide free carbon allowances are legal, in a case brought by refiners OMV, Esso Italiana and big chemical firms.
Analysts say the case is unlikely to affect prices on the EU Emissions Trading System (ETS), at least in the immediate term, because it will not change the overall number of allowances on the market.
However, the principle of how free permits are given to energy-intensive industry is contested and any ruling could have implications for future allocations of free permits for firms considered at risk of leaving Europe because of extra energy costs resulting from the ETS.
The legal challenge was brought by a group of refiners and chemical companies including DOW Benelux, Borealis Polyolefine, OMV Refining & Marketing, Esso Italiana and Api Raffineria di Ancona.
In linked cases begun in the national courts of Austria, Italy and the Netherlands and referred to the top EU court in Luxembourg, the companies challenge a complex calculation, known as the "correction factor", carried out by the European Commission to determine allocations of free allowances.
Through the application of the correction factor, they say a smaller number of emission allowances was allocated to them than they believe they are entitled to.
The advocate general will deliver only an opinion on Thursday, but such opinions are in a majority of cases accurate predictions of the final outcome.
That decision, which is likely to be several months later, will be final with no right of appeal.
Officially, neither side will comment on active legal proceedings.
Speaking on condition of anonymity, one EU source said an irony of the case was that even if the energy-intensive industries win their arguments, they will not necessarily receive more carbon allowances.
Trevor Sikorski, an analyst at London-based Energy Aspects, said the outcome of the case would be unlikely to impact carbon market prices on the ETS.
"Any increase in free allocation would result in a reduction in auction volumes - so the impact would be less industrial buying and potentially more (industrial) selling but that would be offset with the reduction in (auctioning) volumes," he said.
The correction factor argument applies only to the period to 2020. After that, free allocations to energy-intensive industry will be determined under new rules following decisions on proposed EU reforms to how the ETS is managed.