The package includes a controversial payment to Elsenhans offsetting a federal luxury tax on "excess parachute payments," a perk that Sunoco's filing in March estimated would amount to $8.3 million. Sunoco said that perk was agreed upon when Elsenhans became chief executive in August 2008.
"I think it's big, but it may not be unusual," said Eliezer M. Fich, an associate professor of finance at Drexel University's LeBow College of Business.
Handsome golden-parachute packages are standard in the corporate world, "for better or for worse," said Charles M. Elson, a University of Delaware finance professor and corporate-governance expert.
Elsenhans earned $1.2 million in salary last year, but with stock awards, pension, and other compensation, her total earnings amounted to $8.2 million in 2011.
Over the last three years, she earned $21.8 million, according to the company's filings.
Elsenhans, who worked for Royal Dutch Shell in various executive roles before joining Sunoco in 2008, inherited a company whose weaknesses became urgently clear as the nation's economy sank a few months after her arrival. She reduced Sunoco's assets by two-thirds, selling off its units that manufacture chemicals and metallurgical coke and, finally, its refining operations.
Her efforts to rein in costs and to exit the business that has defined Sunoco since it was founded in 1886 won plaudits from investors but angered many employees and community leaders.
Executives who are brought in as turnaround experts often receive substantial cash rewards if their companies are acquired, said Drexel University's Fich.
The amount of her compensation "suggests she came in with a mission and she's done what she was supposed to do," he said.
Elsenhans' package includes the immediate vesting of outstanding options in shares of Sunoco and its affiliated pipeline company, Sunoco Logistics Partners L.P., which Elson said is a standard going-away perk to an executive of a company that is being sold.
Elsenhans will also receive the estimated $8.3 million "tax gross-up" - a payment that companies make to cover an excise tax that Congress in the 1980s imposed on excessive golden parachutes.
The excise tax kicks in when the severance exceeds a standard of triple the executive's average salary and bonus.
Last year Walt Disney Co. changed the contracts of its top executives to remove the perk after it had come under fire from shareholders. Gross-ups are controversial because they are expensive and not linked to performance.
Sunoco stopped including gross-ups in executive contracts in November 2008, three months after Elsenhans was hired. So only Elsenhans will get the perk when the company is sold.
Sunoco said the terms of Elsenhans' package had been previously disclosed.
"These plans are designed to incent management to make decisions to stay aligned with shareholder interests and are a common practice among major corporations," Sunoco spokesman Thomas P. Golembeski said in an e-mail Thursday. "And a significant amount of shareholder value has been delivered."
Sunoco's shares, including a spin-off of SunCoke Energy Inc. but not including dividends, have increased about 43 percent in value since Elsenhans took control in 2008. That gain came at a time when refining in the Northeast was challenged.
Though Thursday was her last day as a member of Sunoco's board, Elsenhans will make a quick transition to another boardroom.
GlaxoSmithKline P.L.C., the British pharmaceutical giant with a Philadelphia presence, named her Thursday as one of two new members of its board.
Her compensation on the Glaxo board will be about $120,000 a year.
Contact Andrew Maykuth at 215-854-2947, @Maykuth on Twitter, or email@example.com.