When Vicki Hollub stood up to speak at Occidental Petroleum’s annual meeting last Friday, she knew she was facing a skeptical audience. After three years as chief executive, she had just agreed the most ambitious move of her career, the $56bn acquisition of rival Anadarko Petroleum, and many investors feared she was overreaching.  Buying Anadarko, one of the largest US independent oil and gas groups, with assets around the world from Texas to Mozambique, will double the size of Occidental. It will also saddle the company with debts of around $5obn, in return for a business that has been failing to cover its capital spending from its operating cash flows. Ms. Hollub promised billions of dollars worth of cost savings and productivity gains from the deal, but many investors remain skeptical that she can deliver.

“It is simply outrageous,” said one top 10 shareholders before the meeting. The deal poses several operational risks as well as putting enormous pressure on Occidental’s balance sheet, he warned. Investors’ lack of enthusiasm for the deal was reflected in Occidental’s share price, which dropped to a 10-year low as Anadarko accepted its offer.

Addressing around 100 shareholders in a windowless conference room in the basement of the company’s Houston headquarters, Ms Hollub insisted that the deal was “a unique transformative opportunity” for Occidental. “We will get those synergies” from Anadarko’s assets, she said. “We can operate them better than anybody else. We are the rightful owner.”