Halliburton equipment at an Alvarado, Texas, equipment yard in June 2015. The merger, which would unite the second and third largest oil-field services suppliers, already faces a growing list of antitrust concerns in the U.S. , even as the slump in oil prices complicates the firms’ efforts to find buyers for any assets that might need to be sold to assuage regulators. The European Commission, the EU’s top antitrust authority, said Tuesday it would open an in-depth probe into the merger after its initial inquiry revealed that the firms “seem to be close competitors, both in terms of tenders and in innovation.” Margrethe Vestager, the EU’s antitrust chief, said her agency “has to look closely” at the deal to ensure that “it would not reduce choice or push up prices for oil and gas exploration and production services in the EU.” Such in-depth inquiries are common for large merger […]