The oil industry has said the Deepwater Horizon rig catastrophe was a unique event, the result of an unprecedented series of missteps that are unlikely to be repeated. The recent history of offshore drilling suggests otherwise.

In the months before and after the rig exploded and sank, killing 11 and spilling millions of barrels of oil into the Gulf of Mexico, the industry was hit with several serious spills and alarming near-misses, some of them strikingly similar to what happened aboard the Deepwater Horizon.

A blowout off the coast of Australia left oil flowing into the Timor Sea for weeks. An out-of-control well in the Gulf of Mexico dislodged a 4,000-pound piece of equipment on the deck of the Lorris Bouzigard drilling rig as workers scurried to safety. A gas leak in the North Sea aboard a production platform came within a rogue spark of a Deepwater Horizon-scale disaster off the coast of Norway.

Data from regulators around the world suggest that after years of improvement, the offshore-drilling industry's safety record declined over the past two years.

The Wall Street Journal reviewed statistics from four countries with large offshore oil industries and modern regulatory systems: the U.S., Great Britain, Norway and Australia. (A fifth, Brazil, declined to make its data available.) Each country uses different approaches to measure losses of well control or spills, but they reveal a similar trend.