(Bloomberg) -- Abu Dhabi National Oil Co. dropped its planned $19 billion takeover of Australian natural gas producer Santos Ltd., walking away from an ambitious effort to expand overseas after failing to agree on key terms. A “combination of factors” discouraged the company’s XRG unit from making a final bid, it said Wednesday. The decision was strictly commercial and reflected disagreement over issues including valuation and tax, people familiar with the matter said, asking not to be identified discussi ...