Four years later, BP is a much smaller company

Shares of BP (BP) have gained about 15 percent in the four years since its Deepwater Horizon disaster on April 20, 2010. The oil rig's explosion spilled more than 200 million gallons of oil into the Gulf of Mexico in one of the worst environmental disasters in history that left 11 people dead and wreaked incalculable environmental damage.

That stock price increase, though, is less impressive than it sounds.

CEO Robert Dudley, a personable American who was named to the job after the disaster, has shrunk BP through assets sales that have raised about $50 billion in cash while cutting the company's oil and gas output by about 20 percent.

Dudley's appointment was one of many changes BP implemented after the disaster. He replaced Tony Hayward, a Brit whose aloof manner was blamed for exacerbating the company's public relations problems at a time when it needed all the help it could get.

Still, the environmental impact of the 2010 spill lingers. A report issued by the National Wildlife Federation noted that bottlenose dolphins and sea turtles continue to die in record numbers. And the human toll keeps mounting among thousands of Gulf Coast residents who've been suffering from a wide variety of ailments in the time since the disaster.

For those folks, April 20, 2010, is a day they'll never forget, no matter how high BP shares ever rise.