Google Finance - BP, VFINX,  VGENXAs happens with stock charts, this one is likely to be out of date even before I get this post published.  But here’s Google Finance’s chart comparing the stock price of British Petroleum (in red), an energy-stock index fund (in blue) and an S&P 500 index fund (in yellow).

Since the oil spill in the Gulf in late April, BP’s stock has tanked.  Meanwhile, the broader stock market has inched downward; and the energy mutual fund, dominated by big oil and gas companies, has done only a wee bit worse than the broader market.

But remember, BP (in red) is a significant part of the energy index fund (in blue).  When I pulled BP’s trend out of the blue line, it looked to me like the recent trajectory of the energy index over the last few months, excluding BP, almost perfectly mirrors the broader market.

What I take from this is that — with the exception of BP, which has certainly taken some lumps — the biggest environmental catastrophe in American history is having essentially no impact on energy stocks.  Big oil companies, in the aggregate, are considered no riskier an investment now than they were two months ago, and no riskier, really, than the stock market average.

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Which strikes me as odd.  If the Gulf disaster teaches us anything, it’s that drilling for oil — and, in particular, the extreme deep-sea drilling that’s a growing part of many oil companies’ production portfolios — is an incredibly risky business.  And while I suppose you could argue that a spill by BP doesn’t affect the odds of a similar accident for Shell or Exxon, you’d think that a spill of this magnitude would clarify that both the the likelihood and the costs of a major spill are higher than almost anyone had thought.

Still, investors apparently perceive the Gulf catastrophe narrowly: as a BP problem, not an oil problem.  That strikes me as risky thinking.  There’s no solid evidence that other companies are free of the safety failures that plagued the Deepwater Horizon.  (See this article for an amusing account of other oil companies’ spill response plans.)  And besides, with operations as complex as deepwater oil drilling, accidents are virtually inevitable.  Sure, years can go by with no major calamities. But when catastrophe strikes, shareholders — like the rest of us — get burned.

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This post originally appeared at Sightline’s Daily Score blog.