The European Commission's antitrust arm will use the next four weeks to pore over the specifics of the merger between Google and DoubleClick to ensure that it falls within the boundaries of the EU's strict laws regarding monopolies.

A deadline of November 13 has been set for the EC to make the decision whether or not to approve the deal or open a wider inquiry. If it chooses the latter, a final decision on the merger may be delayed until the spring of next year.

Google's rivals including Yahoo and Microsoft have attempted to block the merger by lobbying regulators to reject it. Both claim that with DoubleClick in hand, the Mountain View, Calif. search giant would have an unfair advantage in online advertising.

However, Google says that such accusations are unfounded, and that large portions of DoubleClick's business would not change. However, even with US approval -- which looks more likely than that of the EU's -- the merger may still fail.

That is because certain regulations within EU law require that any company that registers more than 250 million Euros in international sales that wishes to merge must get regulatory approval from local authorities to operate in the region.

Out of the big three, Google's ad deal is the only one that has not yet gained regulatory approval. Both Yahoo's buy of Right Media and Microsoft's purchase of aQuantive have both made it successfully through all regulatory hurdles.