Six months ago, on April 20, BP's Deepwater Horizon oil drilling rig exploded in a fiery mass that killed 11 men and led to the worst oil spill in U.S. history. Around 200 million gallons of oil — about 11 times more than the Exxon-Valdez spill — flowed into the Gulf of Mexico over the next 87 days before BP's fifth or sixth attempt to stop the well finally worked.

This catastrophic spill spread across hundreds of miles of coast despite the best efforts of more than 40,000 cleanup workers, thousands of boats, the involvement of the Nobel Prize-wining physicist who heads the Department of Energy, the input of our nation's national energy laboratories, and BP's expenditure of $8 billion on cleanup. Historically, the dirty secret of oil spills is that only 10 percent to 20 percent is ever cleaned up under the best of circumstances. This spill was no different; approximately 10 percent of the oil was removed by the cleanup effort, according to government estimates.

Six months later, what have we learned from what may be the worst environmental disaster in U.S. history? There are at least three big lessons.

First, offshore drilling is a risky business that can cause expansive economic harm and widespread environmental damage. In announcing the recent decision to restart deepwater drilling like BP's well — a wrong-headed decision, I believe — administration officials have acknowledged that we cannot ever eliminate the risk of oil spills entirely. In other words, some spills are inevitable.

Now that the spill is no longer on the national news every night, let's not forget how bad this one was. More than 600 miles of Gulf Coast were hit with oil, thousands of birds died, 1,000 rare sea turtles either died or were severely oiled and hundreds of square miles of sensitive marsh were covered in oil. Tens of thousands of fishermen and tourism workers were put out of work.

The second lesson is to be skeptical of industry and government claims that everything is safe and well managed in the oil business. In newspapers, congressional hearings and TV coverage, we were shocked to learn about the gaps in regulations, the inadequate inspections and safety equipment, the cozy industry-regulator relationships, and the risky decisions that were made on the rig by managers who wanted to drill deeper, faster and cheaper — but not safer. The federal government then told us that most of the oil was gone a month after the spill ended, when in fact much of the spilled oil was still out there.

The third lesson is that we need to end our dependence on oil. This wasn't just BP's string of mistakes. Americans use too much oil — 25 percent of global consumption. This is polluting our air, warming our earth and oceans, making us too dependent on energy from foreign sources and causing us to drill for oil in sensitive places. The extraction, transport, and use of oil and gas across America is an ongoing environmental disaster.

Wherever we allow offshore oil drilling, no combination of technology and/or response methods can definitively protect our beaches, fisheries and wildlife from potential destruction. Yet oil companies and our own government continue to call for more and more drilling in our sensitive oceans. We need to stop and apply the lessons of the BP oil spill. Instead of opening up new places for drilling, we need to protect our coasts and beaches. Instead of letting the oil industry threaten coastal economies, we need to harness American ingenuity to make our cars much cleaner and more fuel-efficient. We need to drive fewer miles by investing in public transit, and shift to wind and solar power.

In the wake of the Exxon-Valdez spill, President George H.W. Bush initiated, and then Congress expanded, a moratorium on drilling that protected our Atlantic, Pacific, and Alaskan shores from oil drilling for nearly a quarter century. Will President Barack Obama find the resolve to restore these protections and lead us in the direction of using less oil? I hope so.

Jon Wong is a campaign associate for Environment Maryland (www.environmentmaryland.org), a statewide environmental advocacy organization. His e-mail is jwong@environmentmaryland.org.